We now live in a world of law suits, I do not know of a firearms manufacturer that dose not recommend against shooting reloads, and some state doing so will void your warranty.
Lee reloading makes a product called the Bulge buster for re sizing the base of brass shot in guns with unsupported barrels, how ever they state not to be used with Glock firearms. Redding makes the G-RX die for this problem in 40 brass, but makes no such statement.
Personally I believe a lot of the myth surrounding shooting reloads or cast bullets threw Glock factory barrels has more to do with Glocks ability to fire out of battery, you always read the unsupported barrel or polygonal barrel as being the problem, how ever many pistols have both issues. And regularly shoot reloads and cast bullets without the famous Glock ka-Boom.
The Lee as well as the Redding Die both work hardens the base of the brass. Now you have a brittle spot at the base, if the round is not fully chambered. In a now much more unsupported barrel because of excess bullet lube, shaved lead. Or other poor reloading habits in reloading for the Glock. Ka-Boom The Lawyers have a field day.
The same can be said about bullets, the manufacturer has no control over the bullet once it leaves the factory, so naturally they will opt on the side of caution.
I have read many posts that cast lead bullets should not be shot above 1000 FPS, however I know many guys that push them much faster.
It all boils down to common sense, If you are loading Blue pills you better know where the line is. Or have a very good health plan.