I've got a DD on my AR, and it's great. The best option, if money isn't an issue, is an Integrated Upper Receiver, but they are big bucks. Whatever you do, go free float (if you wanna go past 150yrds), or if you want to mount an optic forward of the standard upper. Anything mounted on a hand rail, in my experience (even with the DD) will not hold zero (but grips and lights are all good).
My DD would move within 1-2 MOA when my optic was on it, so I made some adjustments and moved my whole package back. Once I bought an IUR, everything went back forward, and it's worked out fine.
Hope it all works out man.