Safe, yes, absolutely in my opinion and experience.
Accuracy... well, they're not a match gun like some of the State Arms guns are. They're just a simple and inexpensive single shot AR upper. Don't expect miracles, but 1.5 MOA is doable, better if you pay good attention to the upper/lower fit, have a good scope, and hand load your rounds. If you're not rolling your own, don't expect match accuracy from anything at all, unless you're buying top shelf ammo. With the SHF upper, I had no problem hitting a 5" gong every time at 400 yards with XM33.
Basically what I'm trying to say is that if you're wanting a very accurate gun, you'll need good ammo, and decent optics. If you're looking for decent and cheap, you're not going to get a match gun. Even the ULR and State Arms models won't be sub-MOA without really good ammo and plenty of work on your part as far as being a good shot, and going past those to more accurate guns will set you back easily five digits when you figure in the scope and so on. Then in a different direction, some uppers such as the Tactilite and Ferret are incredibly accurate with good loads, a good scope, and a great shooter, and we're talking under 1/2 MOA.
If you won't be happy unless you've got a sub-MOA .50, keep saving instead of settling for a cheap solution. You'll need a reloading setup for 50, or you'll need to pay quite a bit for excellent ammo. Or, if you'd be happy hitting a reasonable size target, try out a cheaper rifle or upper with relatively inexpensive ammo and go from there.
It really comes down to what your goal is with this purchase, and there's a lot to consider. Same situation with any rifle, really.