The Lezyne Femto Drive I bought is for the rear and attaches snugly to the seat post. Pressing the lens for 1-2secs lights up the tiny LCD-battery-powered gadget, blinking in different modes as you continue to press the lens. I was amazed at how extra bright this one was compared to previous bike lights I owned years ago (the basic ones the are larger in size).
The tie that holds the lens to the seat post is made of rubber so there's no worry of getting that (precious) seat post from getting scratched.
The Lezyne Femto Drive also sells as a front light (high white color) which costs the same as the rear (PHP 580.00).
Definitely a safer way to bike at night.