The GLK was easy to install on my Glock 19. The laser is very bright but if the temperature is below 55 degrees the performance deteriorates rapidly. It does not like the cold. Also I'm having problems with the switch. This seems to be the weak link in the unit.
Pros: Bright (when it works)
Cons: Not reliable and its temperature sensitive
This review was written in the old system and had content requirements that are different than reviews written today.