For the voltage, it is equivalent to 3 AA batteries... 30ish hours of use. This will slow you down much less than a hub generator. If its placed in center of bars, it won't increase your aero profile. If you put out your palm forward in front of you while riding, you would slow down a lot more than with this fan... and you wouldn't slow down much.

It depends how much it weighs.

Compared to taking batteries out, charging, putting them back in, there is some major convenience in this. Should be way better than friction generators, and easier to take off and add back on if its handlebar mounted.