RDS = red dot sight
D’Oh!!!
i think what you meant is that you don’t like fixed sights and an optic, or an ‘absolute co-witness’?
‘co-witnessing’ just means that you’re able to see the irons through the window or tube of your red dot optic when they’re flipped up (if you have folding sights). if you have folding back up sights that you can see through the window, then they’re co-witnessed by default, whether they’re in the lower third or centered. either way, just fold them down if you don’t want them in your sight picture.
not being co-witnessed means that you can’t see the irons through the optic and will have to remove the optic to use the irons.
in the OP’s case, since he already has a fixed front, my preference would be to go with a fixed rear and lower third co-witness which keeps the sight pitcure pretty uncluttered as you’re looking over the irons to use the dot.
Xavier, I have a Troy on my 6920, and they have kind of been an industry standard for a folding back up sightfor years, and for good reason.
You’re going to be running an Aimpoint M2, and what you need to think about is if you want to have the irons visible through the sight all the time, or if you want to be able to fold the rear so that it’s not in your sight picture.
There are advantages and proponents for doing it either way.
The guys that I’ve talked to who use them for real are saying that having your back up irons ready to go all the time is the way to go. Also, you can use them for more precise shots, putting the red dot on the top of the front sight post and using the rear apeture to align.
So…if you’re looking at a fixed rear back up iron sight (BUIS) for your red dot sight (RDS), then the Daniel Defense or LMT would be my vote.
If you’re wanting a folder, the Troy, Knights Armament (KAC), or Magpul would be good to go. If you’re looking to save some money the Magpuls make sense.
Hope that helps.
I am quite happy with the Wilson Combat Flip ups
low profile when folded down, clean and lock up tight when deployed
If you decide to go for the Daniel defense, let me know. I just got a new xv upper, and am swapping out the fixed for a folding.
I also voted Other because I’m running an A.R.M.S 40L Low Profile and I really like it.
That’s pretty much exactly what I’d post, except that I’m not a fan of the LMT as it’s something I can make for myself with 20 minutes, a hacksaw, and a file and even then it’s big and heavy. I would have said DD or Larue.
I voted Troy. The Sight picture is much clearer with them then with the MBUS. Of course if it is truly a back-up only then go with the MBUS. They will have a Gen II maybe after shot show…it is the same thing but smaller then the current model.
Troy and I see no use for fixed non folding buis sights. Even with a RDS you may want to upgrade to a magnifier eventually and then you will need folding sights. Even if you don’t run a magnifier the fixed sights obscure your field of view. I prefer not to have them there until I need them.
Pat
Also LWRCI is coming out with new sights…its kind of a cross between the troy and magpuls…similar troy shape but rounded like magpul. And not a conventional flip up and down/peep or O-2 sight…its a rotating square with a peep hole on onside and O-2 sights on the other three.
Funny, pretty much the EXACT opposite of what I would say. magnifiers are overrated at best, and I would say that if the rear sight is obscuring your sight picture then you’re doing it wrong. 
I have pictures showing this that should be coming out in a publication in the next month or two.
I tried the co witness thing for a while and just did not care for the extra clutter. I was using the lower 1/3 co witness. Different strokes for different folks. I have been in situations where it was nice to have some magnification.
Pat
Hopefully this is not too redundant.
The Aimpoint is parallax free so looking over the top of the rear BUIS works very well - just not quite as clean a picture as with the BUIS folded. You are not using the co-witness option at this point. A slightly higher than “standard” mount (+.18") for the red dot works good in this case and is called a “1/3 co-witness” setup. Looking just over the top of the rear iron, the Dot will be near the center of the scope tube and the fixed front sight is mostly out of the way and not an issue.
At this point if your red dot goes out you lower you eye that .18" or so and use the irons with almost no lost time. The iron sights are visible in the bottom 1/3 of the RD tube. No need to remove the RDS. [A 1/2 or “Absolute” co-witness setup will also work.]
The Troy or other quality rear BUIS gives you both options. Leave it up or fold down for a slightly cleaner sight picture. When stored in home defense mode - possibly with long intervals between range sessions - it makes sense to me leave it up. Even folded it’s at least on the rifle.
Due to user error, my older Aimpoint, an ML2, died in the middle of a FAL match years ago. I finished no problemo with the co-witnessed irons. I like the Troy folder I have on the rear with a fixed front sight on the A/R, but if my 60 year old butt was going in harms way I would want the BUIS to be fixed.
KAC is coming out with a new front sight to match the Micro Rear BUIS.
After comparing the Magpul, Troy and Midwest Industries low profile model on the counter at a local shop, I chose the Midwest Industries for my 6920. I walked in there planning to buy the Troy, but it was a little heavier and the detent pin was incredibly hard to operate. I’m running an Aimpoint ML2 in a Larue mount (lower 1/3), and I like a rear BUIS that folds out of the way.
I can’t understand why the MBUS keep getting tossed into these comparos. Being plastic, are they really that good? I mean, good enough to park next to a set of Troys and honestly say “yeah, they’re in the game”?
End of the day, I voted other. For form, function, and cost effectiveness, I LOVE my YHM QDS’s. I was going to buy a set of Troy’s for another gun (cuz I do love them too), but I gotta say, for the price you pay the QDS sights are friggin fantastic, so I bought another set. They’re pretty svelt too 
I believe that you can.
When you consider the cost differences, and the fact that they are back-up sights, I think that they compare rather well.
Besides… do you own any polymer frame handguns?
How about pmags. Got any of them? Wouldn’t you agree that pmags outperform USGI mags?
There are some applications where polymer absolutely makes sense.
I believe that as back-up sights, the MBUS is definitely “in the game”.
I would choose MBUS over YHM every time.
in a HD weapon it makes sense to me to have fixed buis with a constant on RDS. Just one less thing to think about.