Love Logitech but this tracker ball is definitely not for ...
936063
Love Logitech but this tracker ball is definitely not for someone with small hands. Used it for about 10 minutes and my wrist was throbbing. Gave it away.
3050754
Bought this track ball and loved it! It has a dedicated Back button, much nicer than having to find the back button on top of the browser and click it, like there was on the Microsoft track ball from years back, but not on the previous Logitec trackball, also a great product. But less than two months after receiving the trackball, that button stopped responding. I contacted the company here in Brasil, and they slowly told me that since I didn't have what is called here a "nota fiscal" (like an invoice), as I bought it in the States through Amazon, they couldn't provide me with the warranty repair or replacement. Very petty and greedy I think for such a well known company. Shame on you, gipping a customer just because you can...!
3736642
They'll never make a trackball as good as the Logitech T-BB13 (the old white one), which this is replacing. I've repaired it many times over the years, but the scroll wheel has finally died :( The M570 was never reliable enough to take over, as many of you know.

Anyway, I think this is the best available trackball that is made today. The "claw" position that this forces your hand into is not as comfortable or natural as I like, but after a few days of use I am convinced that I will eventually grow accustomed to it. The action of the ball, wheel and buttons are all good while their positions could be better. Their orientation needs to be flattened and spread out a little.

I run XFCE on Arch Linux. The device was detected immediately and everything worked automatically except for the phantom 6th button, which I don't care about. No need for any proprietary software as the built-in mouse settings app worked fine for adjusting speed and sensitivity. A simple xset or xinput line in your ~/.xinitrc would work as well.

In short, it's not perfect, but it's the best you can buy today. Let's hope they keep making them.

Added a couple pictures: Why can't someone just clone perfection? (T-BB13) The Elecom is a little twitchy, had to smooth out the motion a bit. (XFCE Mouse Settings)
3526290
Did not work for the Logitech Trackball that it was claimed to work with.  See the other reviews that this does not work as a replacement when you lose your original receiver.  Do not buy it!
3620611
There is many times when it would stop working.  I'd wait about 20 seconds or so for it to work again.  I have no idea why that happens but it does esp. when I need it the most.  Also the back and forward buttons are not in an ideal place.  I have to move my hand to get to those buttons.  Also they should've made the on/off button on top instead of the bottom to make it more convenient.  I used to own a logitech trackball with finger controlled but that one stopped working after many years.  That one was much much better but the price now is almost 400 bucks!  I wish they made a newer model but with the same finger control trackball.
1923883
Worked really well for about a week and then stopped tracking on every surface I tried. I ended up switching back to my old basic logitech mouse because it was so frustrating.

Edit: Customer service is outstanding, they read my review and sent me a new mouse immediately. If this one holds up it's definitely a 5-star product. Will update with results in a few weeks.
3278390
I bought this trackball based on SO many reviews from happy customers who were using it prior to my purchase.  I've messed with these trackballs on occasion in the office supply store, but never actually purchased one.

I've now used this trackball for several hours a day for maybe the last week.  I often work in places where I do not have much desk space, which is part of my personal reason for trying it out.  "Mousing" around without adequate desk space is even more uncomfortable on my wrist than mousing WITH desk space.  And I spend so much time using my computer, that I am now going out of my way to switch around with different types "mouse" devices, including this trackball mouse, my laptop trackpad, and even just "mousing" to the right place with my right hand ... and hitting the track pad ... with my left hand ... just to take some of repetitiveness off my my right index finger.

Overall, I like the this trackpad quite a bit.  It is easier on my wrist, and requires less desk space.

I read several review comments about the track ball seeming to have some "friction" while moving it around.  I experienced this.  So I removed the ball from the case, and simply rubbed the ball against my hands.  Maybe I got a bit of oil on the ball, or maybe I "smoothed" the ball out a bit?  At any rate, this definitely made a difference, and the ball has been very smooth since then.  However, at least for me, and not being accustomed to this type of a mousing device, I almost preferred the LESS smooth surface of the trackball ... to my "modified" more smooth surface.  What I found is that with the ball so smooth, I have quite a tendency to "oversteer" with the mouse.  I suspect that as I get more accustomed to it, everything will be fine.  But, for users who have never used this type of a trackball, you might try it out, first, with MORE friction ... and if you want it to be smoother, you can easily make that modification.
4894646
I used a Logitech wired trackball for 61/2 years and loved it....the wireless version is even better!  Very smooth, fits my hand great and 2 programmable buttons!  Definitely recommend!
4479391
The "fatal flaw" of the buttons acting up -- several reviews mention this, going back several years-- has not gone away. I've used mine and it worked fine for about six months and then the left button started triple clicking nearly all the time. I've cleaned it out, checked all the settings, slowed down the double-click speed, blah blah blah to no avail. Given how often I c&p as an author/editor, this is simply a deal-breaker. I loved the wired version of this trackball, but apparently when they went to wireless Logitech decided to dump the quality I had come to rely on.
4796565
I've only found 2 wireless optical handheld trackballs online.  This was the first I have purchased so far.  I also own a wired non-optical handheld trackball called the Rolee-Polee.  I absolutely love they way it feels in my hand as well as the position of the controls but over time the X and Y rollers begin to slip on the surface of the ball which is why I began to search for an optical version.

This one tracks PERFECT without missing a beat as one would expect from optical technology.  I just wish it was more practically shaped for better functionality.  Although I will say that the dual purpose nature of this mouse for use in hand or on a surface is a neat touch.
2040658
I've worked in computer support most of my adult life. I developed a twitch in my right index finger and a knot in my shoulder from so much use of a mouse and I had to switch to a trackball. I used a Microsoft Trackball Explorer for a long time and absolutely loved it. My backup went belly up about 18 months ago, MS hasn't made them for probably 8 or 10 years, and they fetch a premium on eBay so I was set in search of a replacement.

My first trial was with a Logitech TrackMan Wheel. That worked for a while but the tracking is operated by thumb and you still click with your fingers. It took a lot longer than with a mouse but the twitch eventually returned (imagine involuntarily "clicking" while you're trying to eat dinner).

My biggest problem with many of the devices available is that they are thumb operated (Logitech TrackMan), too large (Kensington Expert), or too small (Logitech TrackMan Marble) and 90% of the trackballs have no scroll capabilities. All that being said, what attracted me to this was fingertip operation, primary button actuation via thumb, and scroll wheel/ring. Added bonus: it can be operated left- or right-handed.

I am EXTREMELY pleased with it. I deduct a star because it's not a MS Trackball Explorer. It doesn't seem fair but the MS trackball fit me so perfectly it is the standard by which I judge all other trackballs.
3641094
This was my first trackball mouse, and six months in, I must say I have zero regrets. Two days and I got the hang of using the ball, and then I just basked in the glory of setting my mouse down wherever I felt like it as I rolled through AutoCad and Rhino. And for maintenance I just spend about 30 seconds cleaning underneath the ball once every three months or so. I now look down in disgust at those pitiful little traditional mice, whose owners have to move their arms this way and that and all around. Not me. I have Logitech Wireless Trackball M570. And it's great.
3617918
Yikes they weren't kidding when they say the trackball is sensitive.  I saw those comments and thought, hey I like a fast trackball.  This thing is like a mouse on speed.  It is impossible to slow yourself down enough to easily control this.  It is not even a matter of getting used to it.  If you use the trackball as much as I do, you'll find this one useless.  If you only used it a little bit, like maybe controlling a Android TV box it probably wouldn't be too bad, but it's corded, so not exactly practical for that either.  I went back and read the other reviews to see if you can set it slower in the mouse settings but found nothing so now it's been put aside as a desperation use keyboard and I've just kept cleaning my old Focus rollerball every few days.  Kind of a shame as I love the keyboard.  Not sure why anyone in their right mind would build a trackball mechanism that would be that quick and thus nearly unusable without providing software to adjust it.  I reduced this to one star, since there is no way to control the trackball speed, I really should have returned this, it's an expensive backup keyboard.
1840606
Second M570 I've owned. I prefer trackball vs mouse when I am working in my office. First one failed after 5 years. This one after 6 months started double-clicking even when I make conscious effort to singe-click. Tested on two separate computers and verified that it is indeed the trackball. I've tested with two other (logitech) mice and they all works fine. I looked online and there are numerous mentions about this symptom. What has been suggested is swapping out the micro switch (2 of them) inside the trackball but I shouldn't have to bother with fixing the product only after 6 months. I've created a support ticket online at Logitech website so we shall see how supportive Logitech's customer service is and I will update. Maybe mine was just 0.1% of overall good product but just be aware.

Update (10/26/17) : It has been 6 days since I've created a support ticket and Logitech has not gotten in touch with me at all. Disappointed indeed.
1327025
I really was interested in the design and capabilities of this Kensington cordless trackball / mouse.  Until now I have used a Logitech trackball and found, as another review did, the Kensington slimblade ball too, too hypersensitive, with no way of adjusting it.  It really distracts from the speed at which you can work.  Hope I can get a refund, as I will try and go back to the Logitech models.
4802905
I have been using Logitech Trackballs for 10+ years. I love being able to "cut the cord". It is sitting on the arm of my recliner as I am typing this review on my wireless keyboard. Very comfortable. I took it to a Software training Seminar last week with my laptop. Everybody else was running their finger over their laptop's tiny touchpads to manipulate the mouse pointer inaccurately. My trackball very quickly and accurately steers the mouse pointer to pulldown menu arrows and increment/decrement arrowheads within the applications.
891787
I have been a user of Kensington trackballs since the early 90s (TurboMouse ADB days!). In those days the driver software did so very much more, like being able to customize each button on a four button trackball to do multiple click types while holding a modifier key, so holding control and clicking was different than just clicking the same button. You could combine modifiers to make lots and lots of click types, so shift-control-click did something different still!  It was wonderful in those heady 68k and PowerPC Mac days before the launch of OS X. After OS X, the software lost these extra abilities. In the years since, Kensington has released few Trackball updates, but I usually buy each one, with the exception of the SlimBlade and the Orbit wired version (I have the wireless Orbit).

I wanted to get this one due to Bluetooth LE support, which is a must for the device to work properly. My Mac supports BT LE and so I was surprised when the documentation stated that a Mac user needs to use the Mouse system pref panel to configure the Trackball. There are two very large issues with this setup the way that Kensington has done it. There is no way to customize the four buttons on the Trackball. There is a choice for which is the primary mouse button (left or right, which seems to be bottom left or right), scroll direction, scroll speed, tracking speed and double click speed. So now my Trackball that professionals use with four buttons has one;y 2 that are usable. The other big issue I see so far is there is no way to check the battery level in the system. Other BT devices can show battery level either through the BT menu extra or in the mouse panel itself, but this Trackball shows it nowhere that I can find.

I still love the device itself as far as input goes, but the lack of customization on a $100 input device is unforgivable. I would not have bought a Bluetooth device if I wanted to use a USB port on my MacBook Pro. The whole point of a BT device is to free up the port, not use it because the coders at Kensington cannot figure a way to make BT LE do their bidding. Kensington, please re-examine your treatment of Mac users! We  are professionals, and we do like to tweak and tinker. Step up and show us you still care!