I can help out here!
I bought one when they first came out and I really liked it. Especially because I could use my original wheels and it had zero drag when not in use. Plenty of power for LED ligts as long as you match the unit to your expected speed. No issues in rain at all. Crazy light weight. Overall they work exactly as billed, but here are the quirks that may turn off some folks:
(1) A little noisy when in use, but if you mount on the back a lot less noticeable. I always felt like it was keeping me company at night so never minded the whirrr...
(2) A bit fickle to mount but if you are handy no problem. You have to get it mounted so it is exactly radial to the axle for lowest noise.
(3) Can get bumped out of alignment if not careful, but easy to hand position back too.
(4) Stay out of the mud!
I have switched to battery lights, but I can highly recommend these if you do not mind my drawbacks above. I found the info on their web site to be very accurate and complete for description of the device and use. I prefered it over having to rebuild a wheel for a hub dyno. No regrets for the 3 years I used mine,