I have a Fastex-style QR on my left strap. I use it every time to get out of the harness. When I adjusted the harness so I could get out of it, it was too loose for me when diving. Maybe I like it a little bit more secure than most folks, or maybe I'm less limber for getting out of it. I used the instructions in the links listed above; I still like it my way.
I considered using a buckle instead, but I already had the QR so I used that. Maybe when it breaks I'll get a metal buckle. One thing about QR is it goes to the same length with no fuss; I'd think one might have to "eyeball" the strap length every time with a buckle to get them even. Or maybe you'd put a dent in the strap from clamping the same place every time and just line it up with that.
I did not sew mine on; I just used the little pieces of inner tube that came with my DSS harness. They're too tight to get anything else under them, but the work pretty good keeping the QR in place if I put them right next to it. So far it hasn't moved at all.
In my case I put the QR on the left because the drysuit valve is on that arm.
I know everybody's just trying to be helpful, but it still kills me to read some of the answers, like "Practice", or "Pull it over your head." I guess you never know if maybe somebody hasn't already thought of some of these things, but sometimes it seems to me people come off a bit condescending. Never mind. Anyway, it seems to me that several of these answers may work sometimes, but not every time. I'd rather have a system that will work in those "What if?" situations rather than just assume I'm going to be able to pull it over my head every time. What if I ran out of air and I have to remain on the surface? What if I'm in a current and only have one hand because I can't let go of the boat? What if I hurt my shoulder and can't wriggle out of it? Now you can say I'm adding another one - what if the QR breaks? Fair enough. But I feel that I've weighed the likely risks and I'm happy with my decision. So far.