Originally Posted by Falchoon

I have a couple of these on the back of my helmets as auxillary lights. You can get them off eBay as well for about half that price. IMO they aren't bright enough to use as a primary stand-alone light, just as an emergency or backup.

There is a much brighter (40 lumens) USB version out now which I have just bought recently - Cycle Design Safety 40 Lumen Rear Light