I have had this light for over 1.5 years. The only thing I have ever replaced were the batteries. I have this light on a KWA USP .45 and it fits very very snugly on the rail adapter, I have a hard time getting this light on the rail adapter and I am not a poorly built person. I believe it would fit better on one of the newer model adapters or a built in rail(at least I never have to worry about it falling off. The light slides onto the rail and clicks into place with no need for any allen wrenches or screw drivers.
This light is quite bright and very durable. As I said before I have never replaced a bulb a lens or anything but the batteries. The batteries are easy to find in stores and easy to install, the entire back end comes off with no tools required. This light has a constant on mode or a blip mode for short bursts of light as needed. Very user friendly as the switch in the back is easily controlled by the weak hand's thumb.
Quick and easy to install
Quick easy battery replacement
No tools required for basic use/maintenance and that translates into speedy battery changes or quick swaps to different weapons all in battle field conditions.
Fits a little too snug on my gun.