just installed a Shark Bite brand valve on a 1/2 inch copper line, so far so good.
On another note I installed some brass gate valves years ago for my main shut-off to the house - that was a mistake and they will be replaced asap with high quality ball valves. (they leaked water into my crawl space resulting in a mess)
it amazes me to see plumbing that is unprotected from possible cold temps in areas that have border line freezing periods...where I live it sometimes hits 20 below and you better have some protection for your plumbing!