I'm not advocating for shark bit fittings, but at the end of the day a shutoff valve has to be in an accessible area. You can't close it up in a wall regardless if its a sharkbite or not. A shutoff valve has the potential to go bad, leak, and so on because its a bunch of seals and moving parts. A sweat joint is the way to go if your closing it up in a wall. You should check on your shutoffs once in a while anyway and "exercise" them especially your main shutoff. The last thing you want is a leak and not be able to shutoff the water because of a bad shutoff that wont budge.