the packaging on my G2X says "not for weapon mounted applications"
As did the packaging on my 6PX. I emailed Surefire about this after I bought it. In short, All we are saying is that it has not been tested and certified for weapon mount.
For that coveted status you must pay more, which I'm sure any LE or military org would be glad to do. And to be fair to the brand, if I'm asked to put my name on a light to be mounted on the end of a soldier's M4 in Afghanistan, I want a few thousand units mounted and fired through a wide variety of rifles, thrown into trucks and off of buildings, dragged through the mud and desert from sub zero to 150 degrees, and generally beaten on in extreme conditions. I would attempt to emulate conditions that a Navy Seal team might encounter, which are quite different from those inside my air conditioned home. I don't live in a mil spec environment and this torch doesn't claim to be capable of performing in one. I have a shooting friend who has sent several thousand rds thru a carbine with a G2X out front, and boy does that thing do a great job of something it hasn't been certified to do. And as for my own personal experience, only 50 rds of bird shot down the pipe at a paper target. Hardly credentials worthy of outfitting a SWAT team. But enough to light up something that goes bump in the night.
As for the $7 mount, not so much. The hex screws are too short to fit around the mag tube so it's mounted to the barrel. Stays secure enough but I wouldn't trust it after 100 rds. I see an Elzetta in my future.