The FTS (A.R.M.S.) mount that Eotech supplies with the G23.FTS magnifier comes with an optionally-installed 7mm riser that can be installed so that it matches the mounting height of the OPMOD (or Eotech EXPS3, or any RDS optic on a riser). It provides co-witness in the lower-third. That A.R.M.S. mount does have a quick-detach lever and it goes on and off pretty easily. I use that magnifier occasionally on four different rifles, including an OPMOD, an Aimpoint T-1 (LT660 mount) and an Aimpoint PRO.
Reportedly, Eotech will be announcing a new/improved version of their magnifier/mount system at this year's SHOT show. 3.25X that is diopter-adjustable, wider FOV, and an improved mount not made by A.R.M.S.
http://www.thetacticalwire.com/story/251869
http://www.shootingillustrated.com/i...-at-shot-show/
http://www.shootingillustrated.com/w.../01/eotech.jpg