I've collected quite a few fans over the years, both mains powered, battery powered and USB powered. Battery powered is really a no starter except for mobile use. Mains powered are usually big and cumbersome, make quite a lot of noise and quite expensive to run when used extensively.
USB powered fans like this one are the best compromise for me. They're built for power efficiency as the power rating from a USB source is quite low. USB 2 ports are rated at 500mA and USB 3 ports are rated at 900mA. This fan draws just 270mA so is well in range for either sources. So it is quite practical to run this fan off a computers USB port. It will also run off 4 AA batteries when needed but don't expect the batteries to last all that long.
It moves quite a substantial amount of air for such a small fan. I was very impressed with this. The problem to me is that it only has one speed setting. Its full power or nothing. I found the level of noise was a little high but not too obtrusive.
Overall, I am pleased with this product but I feel they could have made it so much better if they had a speed setting.