It's very light and sleek looking. Many hours of riding on a charge. Easy to cycle through the different flashing patterns, and it remembers which pattern is active through an off/on cycle. The auto-off works with a couple of the patterns, but I'd rather not use that feature anyway. If someone bumps my bike while it's active, I don't want a "steal me" kind of flashing to start up.
The feature I bought it for, the the brighter "braking" light, works great. When it senses deceleration, it stops flashing and lights up brightly for a couple of seconds.
Since you get both a under-seat adapter and a seatpost adapter, I use it on both of my bikes, it's easy to twist and uncouple it from either mount.