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.