Never dealt with M&A. Have dealt with J&T. Their kits are a fair price, and are all new parts of good quality. Good finish on everything, and nothing junky. They advertise their kits as having Shaw barrels, which I think is a plus. Also they don't charge for using a credit card, which everyone else does. Their upper 1/2 comes all together, no assembly required. Time to install the lower parts and stock is under 15 minutes if you have some experience putting lowers together, and a little more if you don't. There were a few hammer marks on my last J&T upper that didn't thrill me too much (from ham-handed installation of the sight pins)but they touched up okay.
In my humble opinion, nobody's kit is going to be quite as nice as a factory rifle, so don't expect that. Kits aren't all the same quality, so do be careful what you buy, and ask a lot of questions up front about whose parts they use, and whether the kit includes all new parts. But a kit is a good way to have a pretty decent quality AR with all new parts for about $575 or so, including the lower.