Stag is the only and has been the only lefty manufacure that I am aware of. They work fine and Stag overall is a decent builder.
My only experience with the lefty guns- I have a buddy who was working as a private contractor in Bahgdad and I sent him a Stag lefty upper so he could shoot out the drivers side window of the armoured Suburban and not shower the occupants with hot brass.
He said it worked great.
I have seen 1 guy using a Stag lefty on the 3-gun tour, I don't ever remember any malfuntions.
Hope that helps.