As a training aid they are great. Very easy to spot if somebody is doing something wrong like jerking right before they pull the trigger.
I have one on one of the bedroom guns. My thought is this....should something ever come up, chances are I am going to be a little groggy, my hand eye coordination may not be 100% and chances are its going to be dark.
I feel more confident that the laser will aid me in staying on target in that type of situation as well as lighting up the area somewhat. Definately don't see it as a crutch.