Various Issues:

1. The light will arbitrarily turn off with no button presses.
2. The light can not be turned off, even after disconnecting/reconnecting the batteries.
3. Occasionally, it gets into this mood where the light just stays dim all the time, and if I connect the batteries, it will burn through a set in a matter of minutes.

I will say though, that when it is working, this is the sweetest tail light I've ever seen. However, if it's dark, I wouldn't leave home without a backup light, as I've been stranded once with no tail light (that would allow itself to be turned on) already.