For the money buy a go and no-go set for headspace safety milspec will have nothing to do with bolt and barrel only the parts themselves! The remark only goes with building it yourself not a factory build.This was ultimately where I landed as well. I want to build one, but I am just not experienced enough to feel comfortable picking those parts out and I wanted to be sure I had something I could rely on (and at very least call the manufacturer about if I had any issues) before I step into custom builds. I think the M&P-15 is a great starting point to build that experience and start figuring out what I like / don't like.
I reallllly wanted the Colt. But it was also about $400 more than the M&P. Probably shouldn't have been that much more expensive but the damn things are selling like hot cakes right now.