I have the ADM lower and test-fit it with most of my stripped/new uppers.
It fits well with a Cerro Forge (Keyhole forge code) upper.
The DDs I’ve seen lately have splintered-A forge codes, which come from Anchor Harvey.
I’ve generally seen square forge code uppers to be looser, though it depends on the machine shop who finishes them.
I went with a non-forward assist upper for mine.
Fit/feel/finish looks fine since I had the ADM lower Cerakoted FDE to match the upper.
Advantages to the ADM lower are:
* Ambi bolt hold open and release that is very intuitive
* Funneled magazine well for ease of reloads
Disadvantage to the ADM lower is it’s a little heavier if I recall, so not the best lower if you’re looking to shave ounces on an ultralight build. Others would say price as well.