Quick and dirty run down:
There are three criteria that handguns must comply with for MA compliance:
1. The MA AWB. Handguns can't have more than 1 of a set of features (magwell outside of pistol grip, threaded barrel, barrel shroud that allows holding the barrel, weight of greater than 50 ounces, semi version of auto firearm)
2. The EOPS list. Handguns must be submitted by the manufacturer for safety testing. If the handgun passes the test, it gets added to the list. Off list handguns can only be sold if they were here before 98. The penalties for selling off EOPS list are steep, because dealers can be charged criminally.
3. AG approval. The AG has a set of "consumer safety" requirements. They do not provide guidance on how to meet these requirements. Manufacturers are required to self certify that their handguns meet the AG requirements. If they are wrong, they will only find out when the AG starts sending cease and desist letters. Penalties for dealers are steep fines.
So, the upshot is - for owners, only Number 1 matters. Numbers 2 and 3 apply to dealers, and result in increased prices for guns that don't comply.