The main selling point of this though is the handy size and shape - like a pair of reading glasses in a tube - throw it in a bag/pocket and forget about it until needed. Apparently a fresh set of batteries are good for 8 hours use, but that's with the supplied. I'm guessing that with a set of new Duracell cells it would be longer. It's quite hard to test that as nobody's going to use one of these continuously for 8 hours+ and it can only really be judged over time.
The main complaint will be the power of the fan, I'm thinking. It isn't very strong and wouldn't be much use in serious heat but for the average UK day, it's just fine if held, as I say, nice and close to the face. For a few quid I think it's worth throwing in a bag.