Don't have one yet, but I like the features of the Fly6 integrated rear camera and tail light. Normally it over writes the oldest record on the memory card so you never have to manually erase it after uneventful rides. But if there's an indication of an accident (impact plus bicycle angle) it'll continue recording for a short period (30 min?) and then stop so that it'll preserve the record of the crash even if you're incapacitated or forget to turn it off.

A few friends and members of my bike club have them and seem pleased with their performance.