Regarding proofs, many, if not most firearms companies proof their firearms and will apply their own proof marks. In the US, there are no government proof houses, but that does not mean proving does not happen.
Indeed, I doubt the modern value of the proof house - tort lawyers have been very effective at safety. What does a government proof tell you? They serve more to date and establish the history of a firearm than anything else. Can we really brag about the Belgian or Spanish junk that came out during the late 1800's and early 1900's (the junk, not FN or other good manufacturers)? Utter crap came out of those, and other, countries that were all nicely proofed. What about RG revolvers with proofs from the 1960's?
Yeah, Cobra, Jiminez, and others, are crap here, but they're not handgrenades. They won't blow your hand off any more than a Glock will. A Glock that Kaboomed (more exaggerated than anything, I know) likely had a nice Austrian proof mark on it.
Am I against proof houses? Not really, but most firearms manufacturers in the US proof in house - they can't afford not to. And a proof house does NOT detect defects in triggers or drop safety or the like - a proof is no guarantee of safety. They merely establish that the firearm will not explode at a certain over-pressure level.
Again, their most useful feature if figuring out the age and origin (or pass-through history) of a firearm. A Colt with German proofs served in Germany, for example, or a Tanfoglio was made in 1989 because of the date code stamped on it, or a certain Star's age can be determined from Spanish date codes.
Glock's Georgia proof establishes that (almost certainly) their US pistols measure up to the same standards as the Austrian-made ones. Indeed, were they to publish their standards of proof used in the US (which they might have, I'm just not going to look it up), I'd wager it was identical to those required in Austria.
