That thing is an abomination that has no place on an AR. You can get the rear sight with dot scope in several ways. On flat tops you could go with the Colt C-More Tactical red dot (has an integral A2 rear sight) or (for example) an Aimpoint with a flip up rear sight. Forward mounted dot sights (Aimpoint, Reflex, C-More) will all work with the existing rear sight on the carry handle.