This is an internal weapon light and does not restrict holster options. It replaces the guide rod and spring in my Glock 19 (gen4). Just remove the old slide release and put the new one in, takes 2 mins max. Push left or right on the slide release to turn on or off. 400 lumens, just right for inside the house at night. Light is $200, uses 8 - 393/309 silver oxide batteries in series@ at a buck apiece. A little pricey but perfect for my nightstand.