Well that was an enormous pain in the ass.
I got the old valve off, but I couldn't get the compression fitting off...
So I pulled out my faucet puller... Couldn't get the compression fitting off.
So, I pulled out the Dremel and cut the nut off, then started cutting the compression ring... Got it off, got the new Sharkbite fitting in and... it leaks. I nicked the face of the supply pipe.
So, back to Home Despot.
Picked up one of these bad boys because I was working in a really tight area behind the toilet...
Thing worked like a damned champ. Absolute great piece of kit. No wandering, no tightening of a thumb screw, just snap it on a turn it clockwise.
I also picked up a slip union and a stub of copper pipe in case I needed to solder in a stub, but I didn't.
All in all, about 3 hours to do what should have been a 15 to 20 minute job, but that's par for the course.
Oh, and as I was putting it on to do the Dremel cutting, my face shield fell apart. Sigh.
I'm cautiously optimistic that it's going to hold.