Things I liked: This light is BRIGHT! It attaches quite easily, and doesn't budge. The weight feels balanced on my USP, and the switch is ambidextrous, a plus for lefties like myself. Batteries included, of course, and the option to add a pressure switch is a nice touch.
Things I would have changed: As it is, I can't think of any way to improve it greatly.
What others should know: Don't forget to turn it off when you're done. It gets pretty hot.