Had a straight brace (still have it; where in PA are you?), and the only fault I could find, it, and the MagPul folder make it tough to get low enough on the gun for the iron sights.
Went with the factory folder (and a stamp), which is both firm and allows a good sight picture with the irons. If you're not worrying about the irons, then a red dot solves the problem.
I have the HB spring kit in my trigger; it doesn't turn the OEM into a Geissele, but it's quite good for what it is. And cheap; less than $10? It's a little fiddly to install.
Mine has been stone reliable, shoots straight (have a tie plate dangling at 85 yards, and have little trouble hitting it offhand), and magazines are reasonably priced. There are aftermarkets available, but I've stuck with OEM.
There is a lot of good stuff for it, but about all I have is the enlarged operating handle, and a couple quick detach doozits for a sling. The MagPul grip is an improvement.
It's a ball to shoot, and not ammo picky in the slightest. Go for it.
You could go with the 16" Carbine and the OEM stock.
BTW, had a SIG, which was not stone reliable, and took those damned $60 magazines...it was not that much softer shooting, either.
Moon