I have a LaserMax I used on my Smith 5906. I would NOT recommend it though, although it works as advertised.
The carbon fouling was not a problem in limited shooting, and it's not hard to just wipe off the lens with your sleeve. Mine held zero just fine.
I did end up having some reliability problems, however. Also, I never felt the laser was bright enough, and not nearly as bright as some external models, which made it hard to pick it up fast. But the most annoying thing was the switch, which in a holster could work itself into the "on" position, leaving you with dead batteries on the draw. Also, I like pressure switches MUCH better for high stress situations - I just couldn't remember to turn the darn thing on in a hurry, and then I didn't want it left on all the time anyway, so I was constantly flicking the stupid thing on and off during practice, which was annoying.