I carried a '6 Python in a Bianchi Phantom shoulder rig for all of a day once, mostly because a friend of mine was trying to tell me the gun was useless because I couldn't conceal it. (not why I bought it, obviously) It was winter, and it hid fine under my jacket, but it was really just for fun, it'd be a pain daily.
I breiefly had the little Uzi with the snap-on DeSantis shoulder rig as well, although mine wasn't full auto, and I only put it on so that I could look at myself in the mirror and never actually wore it anywhere. That rig felt quite heavy to me with the two loaded mags on the off side.
My .50 DE is one of the few handguns I don't even
own a holster for, because really, why? I once met a bail bondsman who claimed he carried a .44 DE IWB behind his right hip, but the guy was built like a mountain gorrilla, and I didn't actually see him do it, he might have been making it up. Far to bulky and heavy for me, I'm built more like a spider monkey.