I know it's only $20 but it's still a waste of money if it doesn't work. I read these (and other) reviews before I bought this unit so I was very careful not to strip the screws. Getting the alignment to work was difficult and time consuming but it finally was set up correctly. However the first time I shot the pistol the alignment screws fell out and the laser stopped dead. The only positive comment I can give is that almost exactly the same thing happened with another manufacturers unit that cost $40.
Pros: Cheap
Cons: Doesn't work
This review was written in the old system and had content requirements that are different than reviews written today.