There's a lot more to a BCG than just saying that it's "mil-spec". What about the quality of the spring used for the extractor? What about the quality of the staking for the gas key? Those are things that matter, a lot. Probably more than the steel used in the carrier.
And in my experience of one, PSA sucks balls for extractor springs. Just printing "MPI" in the advertisement doesn't necessarily make it quality.
The "G" in "BCG" would apply to spring, rings, bolt, extractor, staking, cam pin, firing pin, firing pin retaining pin, gas key, cap screws, and so on.
Don't think they print "MPI" in the advertisement concerning the extractor spring.
