I don't think M&A "makes" anything, they just distribute.
When I ordered my midlength flattop, they sent one with with a flattop gas block as well. They first tried to tell me that all the flattops came that way, then, when I pointed out that their SGN ad showed many, many flattops and none of them had the flattop gas block (especially my midlength), they told me that they were "out of stock" of the one I wanted but that they'd be "getting them in" again by the time I got the incorrect one returned to them. The truth of THAT statement is open to question, judging by when the UPS tracking says they got the wrong upper back vs when they shipped me the right one (about 7 days difference), but the relevant point is that the implication was strong that they got their midlengths from somewhere else. I'm guessing it's from RRA but of course don't know this for a fact.
As I said, the midlength upper I got from them (finally) turned out to be of very good quality. It shoots well and I'm happy with it. But I recently had to order a LPK and I gave J&T that business.
If you order from M&A, be sure to spell out EXACTLY, in great DETAIL, what you want so there can be no "confusion." As I said earlier, their prices are good and their shipping is very fast if they can manage to stuff what you want in the box.