I'm having trouble trying to count the number of people I know who've had trouble with internal guide rod lasers. In any case it's quite a few. As a matter of fact, years ago, it was a fellow at Glock Technical Support who, first, made me aware of the problem.
Pistol lasers are great training devices; not sure whether or not I'd recommend one for SD combat, though. The aiming technique is different; and a fair amount of practice is required before a user becomes instinctively good with using one.
What's the best pistol laser? I'm going to go with Crimson Trace's grip-mounted unit.