These hardly move any air being powered by a 5v ...
928221
These hardly move any air being powered by a 5v battery and they took forever to ship. Obviously they are for a 12v circuit. They come with male connectors at the end of the wires, so get some female connectors handy and save yourself some trouble.
4632690
I bought these and had them professionally installed in a 1,000 sq ft house. 2 units and they cannot heat or cool the house. They barely blow at all and do not ever shutoff. Upstairs is only 300 sq ft and in the summer it is way to hot. I'm hoping customer service will fix them by sending new units so that i don't have to buy 2 more window units (already have 2 installed).
3082906
Meh. Bought these to replace the AC Infinity fans I bought because those are so LOUD. These are whisper quiet but produce half or less of the airflow of the AC Infinity fans. I guess if you just need very light airflow into or out of your cabinet, these are probably fine. Don't count on major cooling capacity for a larger cabinet with a lot of heat though. They also only run on AC, so if you have any kind of USB temperature control device to turn them on or off, these are not compatible.
70852
They say dimmable but they will blow after a few days.
I ordered the 5 pack and 2 did not work right out of the box. The remaining 3 each blew after approx. a week of use on each one.
Junk.
4879137
This machine blows - or doesn't. It is pretty feeble airflow/pressure and the battery does not last long. I bought this to blow dry my car after washing but it is bot up to the task. It has neither the strength nor stamina for the job. The battery performance is really disappointing. I would not recommend this to anyone as a leaf blower or a blow dryer. I have used it for both and it failed miserably in both tasks.
3150671
This fan did not have much blowing power at all and fell over all the time.  I wanted something portable that I could use for agility trials to keep my dogs cool and this just was not effective.  I ended up getting RYOBI portable fans, which I'm happy with.
3751452
I bought this to use when traveling.  If you are not traveling, why not buy a fan that uses household AC current and gives out a lot more air?  I carry a portable fan for travel in case I am visiting someone's house or staying at a place where I need a portable fan.  I've had one for years from West Marine that uses AA batteries as well as an AC adapter, and it puts out plenty of air.  I thought I'd look around for a spare, but the one I have is no longer made.  So I bought this O2COOL fan.  I am disappointed.  First and foremost, hardly any air comes out of this thing.  I use AA batteries with D-size adapters.  Why require a screw to open up the battery case?  Why require D batteries for a portable travel fan?  D batteries are tremendously heavy.  This thing is useless.
3033540
Not the 4 pin I was expecting, but I can make them work. Good for moving air but not for high pressure  - IE: doesn't work well blowing through a heatsink
3309624
These bags do not hold out the air.  I use other brands also and have never had this problem before.  These bags do not hold out the air. I would never buy these again.
2720909
the fan hardly  blows air. On high speed is like its on low.
196685
Ordered two of these units for large automotive storage facility with over 3K cars and trucks. Fully charged and tested use. Both units operated only 5 to 10% of the time. Measured voltage at clamps and they had ZERO output. Suspect faulty internal protection design. Returned both units as defective.
1868756
I wish they weren't just 1,200 RPM, but they are only 3pin. They easily move air in and out, and you can't even hear them if there is ANY noise in the same room.
2880529
these really isn't a speed controller but more a power controller. All it does is reduce the power to a device. I didn't work with any of my power tools. I tried it on every tool I have that is corded. It did work on my fan though. But again its not a speed controller just a power reducer. With my fan on low and the controller set on low. my fan would turn very slowly, but they motor from the fan wants to pull the appropriate amount of power it needs for that setting and they motor is just whaling for it. It is louder that if I put it on high. I just didn't trust it and was afraid it may cause an electrical fire.
1913800
I couldn't get these arctic fans to work as pwm fans. Most, pwm fans put out a small voltage of 1 or 2 volts on the pwm pin, that if you touch to ground the fan goes to low speed. These fans put out a full 12 volts on the pwm pin, and when you connect it to ground it does absolutely nothing. The fan simply stays on at full blast no matter what you do to it. 0 stars
425266
Fans are very, very weak and consequently, this fan pushes very little in the way of air under the sheets.
2524027
They aren't kidding when they say these fans are SILENT! I can't hear them from five feet away.

Pros:
+ Silent.
+ 40mm
+ Comes with a 2pin to 3pin adapter. A nice thought I guess.
+ Does what I need it to do.

Neutral:
~ Doesn't move much air. I didn't expect much from a 40mm low RPM fan, but if you're running high-performance 1U or 2U servers don't expect these fans to keep up.

Cons:
- Short cable! It's only about 3.5" long, if even that. I had to solder the old fan's wires onto this fan in order to make it reach the controller.

Overall:
Great little fans, time will tell how long they'll last in my Baystack switch since they're only a sleeve bearing. They don't move much air but they'll get the job done for switches and little stuff. If only the wire was longer!
3561127
These would be wonderful if they only had more power. I know that there is a disclaimer that in winter months the light is only able to charge them in a minimal way, but I've been charging them in the California sunshine and have only managed to get a couple of hours out of them. They are pretty much useless as Christmas decorations.