"Legal" is the wrong term to use. Most handguns are LEGAL in MA. Not all of them can be sold by a dealer, though, but that's not your problem.
The SR9 probably is compliant, although you can bet your ass the MA version is going to come with a garbage trigger on it compared to the usual 5-6 pound one it normally has. Nothing stopping you from buying one and repairing the trigger, though. You're also stuck with 10 round mags, as there are no prebans for this gun because it's too new.
-Mike