I have one of these on my P30 LEM. It's great - as you can see, it has two screws and three screw holes, they fit into the front two holes on the P30 rail. I tightened them down pretty good, tight plus a half turn or something close. As its plastic you don't want to over tighten it. The actual fit on the rail without screws is quite tight, so I don't think you'll have an issue - give them a quick look before and after a good range session, but I've shot probably 600 RDS with it on, and they haven't come loose at all. The lens did come unscrewed a bit within the first 25 rounds and the light / laser shut off, but it probaby wasn't too tight to begin with, as after figuring out what the issue was, it hasn't loosened up since.
As the laser is offset from the bore both laterally and vertically, pick your zero range and realize you'll get higher hits in close and lower hits further out. I zeroed at 15m and the dot is pretty much on from 5-25, give or take an inch or so. At contact to 5, the laser is noticeably low compare to POI & Iron sight picture, but that's to be expected.
My only gripe is the easy access to only a single light/laser combo (aka, you program it for either light, laser, or both, with the laser either steady or pulsing and the light steady or strobing). It isn't hard to switch them really, but would be nice to have a least two modes easily available while operating the pistol (aka, two operational buttons, one for both light & laser, one for just laser).
But I just set it on steady light and pulsing laser and figure I, good at night and daytime the light won't really matter.