ARMS, item #22M68, w/ no spacer, will co-witness the Comp M, or Comp M2 (ML/ML2 also) w/ your "b.u.i.s.".
The 22M68 w/ the newer "cantilever" spacer will co-witness w/o a SWAN Sleave. And will place the optic out front in its most desirable (by many) position.
The SWAN Sleave w/ the 1/2, full, or new "CL" spacer will mount the optic too high to co-witness w/ your SWAN Sleave, usable, but won't co-witness.
To use the 22M68 mt. and a SWAN Sleave, and mount the sight out front you'll need the ARMS item #'s 38S, or 38S-EX.
38S=slightly longer than the flattop (8.46" OA)
38S-EX=to the front sight assy. (w/ non-M4 handguards only, too low)(14"OA)
Can't speak intelligently on the GGG or Knights mt's, so I didn't at all, but they are options that are liked, just not by me.
The M2 and M are nice sights. I own both the M2 and the older M. I like the M more, I'm used to it and its slightly smaller. But, the M2 has CET tech. that reportedly allows the sight run for "10K" hours(?, unproven in my book) But both scopes are excellent scopes.
BTW I also own the Reflex 1, and have often had problems w/ the dot washing out on very bright days or indoors w/ the muzzle covering bright walls and/or my Surefires (6v/9v) on. So I replaced mine. Still have my Reflex on a "fun-gun" suitable for range time.
Feel Free to EM.
Hope this helps, LOLk, SUL2.
ed. for sp.