I bought a similar one on the 'bay for about half that price. Decently bright and I liked the flashing mode since I usually ride during the daytime, but it would switch modes (or off!) when I hit a bump.

Not really designed for bicycle use I suppose, so I sent it back and got a full refund.

Replaced it with a blinky that's USB rechargeable and haven't looked back (except to change lanes, of course)...