I'm just going on what my plumber says. I used sharkbites and my plumber and his buddies spent like half an hour telling me why they suck. Apparently the issue is that the rubber inside the fitting breaks down, then goes into the pipe and ultimately ends up plugging something up
Sharkbites will get you through a leak and make it work again, but you want real crimp on fittings to do any new work or repair work.