Pumpkin, I would feel safe in shooting +P+ plus ammunition in a Glock.
Several years back I was given several cases of Hirtenberger +P+ sub-gun ammo and put a couple of thousand rounds thru my G17, with nary an issue.
I also fired a few thru a Ruger P94 and within a couple of hundred rounds the barrel shroud started developing a crack. The gun was sent to Ruger and a new barrel was installed free of cherge. The gun also came back with a nice note telling me to no longer shoot that stuff thrugh their gun, Thank you very much!
I thought ALL manufacturers recomemded to not shoot reloaded ammunition at all. Their way to void warranties.
With Glock, I belive the issue is with most reloads being lead and lead not being compatible with the polygonal rifling used by them. The lead smears on the rifling and fills the grooves, causing pressure to climb to unsafe pressures. That is why reloaders replace the barrel with a conventionally rifled barrel. So the lead has something to bite into, not cause of quality issues.