i prefer the right-handed uppers. they work just fine and believe it or not, i think it's better ergonomically for left handed users than right handed users because...
with my left hand on the pistol grip, my index finger can reach the bolt-release, but
with my right hand on the pistol grip, my thumb cannot, so i have to take my hand off the grip and yank the charging handle OR take my left hand off the foregrip to slap the bolt-release.
i've never been hit with a piece of my own brass, so no need for a brass deflector bigger than the one built into the recevier.
the only thing where we have a disadvantage is in High Power competition when you're single-feeding rounds in the prone position.