I bought this laser just to see what a cheap one would be like. Installation was a snap. (Though it does require a JCS spira or fit grip - I used the spira which I do like better than the stock grip). You basically slide the laser into the mount and tighten it down. Once its tightened, it has a push button that gets depressed and turns the laser on. This keeps the laser on constantly, which is not good.
After playing for an hour the laser ran out of juice (from being constantly on I presume), and the power of the beam left something to be desired. I plan on buying a real laser and custom fitting it to my gun, but overall if you are playing indoors in a dark room or MIL-SIM scenario, its a good cheap laser.