I adjusted pretty quickly, though
927481
I purchased this to try and relieve tennis elbow symptoms, as I spend 8 or more hours per day at a desk and 30+ years of doing so starts to take its toll. I adjusted pretty quickly, though, and right out of the gate I was probably 85-90% as efficient as I was with a traditional mouse. Now 4 weeks later I am probably at 95% or higher - though for very fine mouse skills are still a bit slower, but are a very small part of what I do. The good thing is I between adding this, a Belkin WaveRest Gel Mouse pad,and rearranging my workarea to ensure I'm keeping my elbow at 90 degrees, I've seen significant improvement in symptoms. And I notice it even more when I return to my laptop and I'm on for a few hours. So overall I'm very happy with it. One note, I mistakenly ordered a small not realizing there are different sizes. My hands are actually large, but it doesn't seem to make much of a difference.
2289258
Took a few seconds to figure out how to adjust the weight settings, which is about how much time it takes to change weights.

Oh and they got to my house in HALF the time they were supposed to!

GREAT DEAL!!
4406402
The button got stuck within a few hours of use. I am using it as a standing desk, which I place on my regular desk in order to create the necessary extra height.

Updated: I've upgraded from a 2 star to a 3 star. Could conceivably be 4 star. The issue I had is that one of the buttons got stuck within a few hours.  I purchased a new spring from the hardware store, removed the leg, and was able to fix the button. Its annoying that it needed fixing so quickly, but on the other hand, its simple design makes it fairly easy to fix if you're willing to try.
106177
I'm medium to small, chest- size wise.  This binder is pretty easy to adjust, if you don't mind taking time with all of the little bra hooks. I find it pretty comfortable to wear, and it does a good job at getting my chest really flat.  The 3 elastic strips on the side are a bit awkward- if you're binding tightly, they chafe a bit.  I've sewed a piece of spandex underneath them, so they don't touch my skin, so now it's perfectly comfortable.  I would recommend this for anyone on a budget.
883026
I had to modify it a little bit. No complaint though because it was a great deal.
2674710
Speedy delivery, product works, but wished it could be adjusted to fit better.
2112603
After a few months it started to get forward. About 1 minute per day. I have to adjust it everyday,
887982
took a couple days to get used to pockets different from my old bag.  really like the quick-adjust strap.
1277608
Took awhile to adjust the settings correctly, but I like this mouse.
995343
It took literally a minute to learn to use this and another few minutes to finish tuning the drum set.  At the end I decided the tone wasn't quite what I wanted and it was super easy to lower the setting a couple notches and re-tune.  I can't say yet how well it will hold up, but I'm really happy with the results so far.
516178
I had to take a small jeweler file and open up two of the bolt holes on the mount, because they were slightly offset, in order for the mount to bolt on property . No big deal for me, but others might not have the tools to make the adjustment. Over all not bad for the money though. Would buy another one of needed.
4288075
What I've seen so far is that I have more control at longer distances, quicker response.
1693921
Really hard to adjust, but once adjusted it worked pretty well.
708141
Performs as advertised within a couple degrees of accuracy.
2062986
It took a while to learn to adjust this for using, since I'm short (4'9") and wear progressive lenses.  Initially frustrating, but soooo worth using once I figured it all out.  I would definitely recommend this product, though it may take some time to adjust it. It can definitely be adjusted for your visual and body size needs.
4113410
Easily adjusts to your needs. Great quality.
4886344
I was surprised that these are a bit larger than I expected. Installation was quick and easy. I think they will be very easy to bump out of alignment, but they're also very easy to adjust while on the bike--just reach down and tweak it. I ordered these over another option that required a hex key to adjust (and therefore was probably much more likely to not need re-adjustment) because I wasn't sure how one could ever get it set correctly while on the bike.

I ordered the two-pack, and installed both. I can see where the right hand one would be most useful if you were racing (which I'm not), but I figured if I broke one, I'd have a spare. Also, there are times (albeit rare for me) where the right-hand mirror could be useful, especially if passing someone else.

They do seem a bit pricey for what they are though. I'd be happier with them for about $10 less, if I could deduct a half star for that I would.