Doug,
This is my first post here, but I think I can answer this question. I'm still trying to digest the jargon and acronyms, so please understand that I am a newbie.
What you described is the Tactical Carry Handle. It is sold by Rock River Arms. I just purchased my first AR and it has this type of 'handle'. From what I have found out so far, it is kind of limited in it's usefulness. I think that it was originally intended to be used to mount an Aimpoint ML2 red dot. The only way to mount the Aimpoint and co-witness the iron sight is to use the mounting ring that Aimpoint no longer includes with the red dot. I called RRA and they have the rings. I bought one for $12. I mounted it last night but I haven't shot with the Aimpoint mounted yet.
They list the Tactical Carry Handle in the catalog for $175.