Nothing wrong with Sharkbites or the equivalent competitors' products if the pipe is deburred and pushed in to the proper insertion depth.
However, the root of the problem with being able (or unable) to solder seems to be a leaking main shutoff valve. I'd simply install an additional shutoff valve a foot away from the existing one. Use a valve with a compression fitting on each end and you won't have to worry about water in the pipe or soldering.
Sometimes that is not an option.
I had a wall heater that failed and there was just a stub coming out the wall. After wasting an hour trying to solder (and risking setting the wall on fire) I slapped a sharkbite on it and its been fine for 9 years now.
Draining out a heating loop in the middle of winter that holds over a thousand gallons of water was not an option.
