I have two M&P22 Compacts, with a group of rounds through both. Among other things, I use them as "loaner guns" during NRA Basic Pistol. I also like them at a new-shooter introduction gun.
Great weapons. Here are the biggest personal reasons why I like them over the SR22:
1. Normal manual of arms: the safety/decocker on the SR22 works
opposite of how other safeties work, i.e.
down is on, up is off. This can be confusing to new shooters, and a "habit" you need to "unlearn" for other weapons. The M&P22 has a normal down/off, up/on safety.
2. Full size analog: the M&P22 Compact is within a whisker or so of the M&P Shield in terms of size, and has the same controls, sights, etc. It's a great companion trainer to the full-size gun, if you so choose.
3. The mag safety takes
literally 30 secs to remove, and doesn't alter the gun in any way.
The M&P22 Compact is a huge improvement over the full-sized M&P22. The Compact is made here in the US, and has an aluminum alloy slide. The full-size M&P22 is made by Walther (Umarex, actually), and has the zinc alloy (ZAMAK) slide.
One thing to keep in mind, and it might be a deal-breaker for you. I don't know the particulars of MA law, but the M&P22 Compact (both the suppressor-ready version and the "regular" version) has a threaded barrel (removable barrel "cap"). I don't know if that's a no-go item for MA. I know you can find the SR22 with a plain barrel.
As another plus, with a 3.56" barrel, the M&P22 Compact keeps even regular bulk-pack ammo subsonic, and it's a very quiet suppressor host.