I got the tail-light version of this, and it's amazing.
1) The LEDs are extremely bright and can be seen from very far away at night.
2) It has 6 modes (continuous on, flashing fast and slow, going up and going down, and a random individual LED mode that looks as if the light is having a seizure).
3) The silicone strap makes sure it wraps securely around the seat post without being bounced around every time you go over a pothole. Also, it goes on quickly, and comes off quickly.
4) The AAA batteries are easy to change. (The silicone casing is a bit fiddly when you try to put the lights back in, but this is easily circumvented once you realise it's almost impossible to tear it).