I hate being the guy that keeps saying this, but a piggybacked MRD sucks. I say this having a bit of experience with this topic.
The “Chin Weld” that the piggybacked optic forces you to employ is sub-optimal. Optimal is having an identical sight line. Next best is having a slight rotation of the gun without compromising cheek placement on the stock. The height of the optic over bore makes many unconventional and covered/supported positions more difficult than they already are, as well as introducing a whole other aspect of hold-overs at close range. There is a reason that the offset MRDs are popular with those that have the option. Sure, you can use a piggybacked MRD, many of us have, but most of us have also decided that if the option exists we will go a different direction.
-Reticle, I wanted a red Chevron.
If it’s what you wanted, I am sure that it fills your needs.
However, if you want the reticle to help you perform certain tasks at distances between 200 and 300 meters, it blocks a lot of the target, which might not be all that eager to show much of itself.
The crosshair reticles such as in the “J” models are much more precise at those distances, and the “H” models are almost as precise, but much faster in use, especially in waning light.
-Eye Relief, I compromised here. The 1.5" eye relief on the 31 series is short but I liked the size/weight and the power of the 31 series as compared to the 11 series (3.5 power)
Eye relief is a critical part of dynamic shooting, especially from unconventional positions. If weight is an issue I would rather give up one degree of magnification and go with one of the 33 series ACOGs (if you are dead-set on an ACOG). A little more eye-relief and exit pupil makes the optic much easier to slide into when all else is not perfect.
Good luck with your purchase. I am sure you won’t be dissappointed with any ACOG.
As long as you choose one that fits your needs 
Now, before anyone gets grumpy, I am not trying to tell Noodle that his optic sucks and he should sell it or he is stupid. If the thing works for you, great, keep it and cherish it, and pass it on to your offspring. However, the ACOG line has improved quite a bit since the TA31 landed a military contract (and even then it wasn’t the best option, in my humble opinion). I own 2 ACOGs (TA11s), one of which is mounted on my game gun. I do, however, recommend something other than an ACOG for a more rounded application.
USMC03 has a good article regarding ACOGs, I’ll see if I can dig it up and post a link to it.
ETA- Here is that link.