Have both. Happy with both. Have run thousands of rounds through the full size, a few hundred through the compact. Both run well with, as Kaldor noted, a bit peppier ammo. If you want to duplicate the feel of the FS M&P, get the original .22. If you're looking for a smaller, lighter pistol, with a smaller grip, get the compact. If I had to keep only one, I'd probably go with the smaller compact (unless, again, I wanted to more/less duplicate the feel of the FS).
Have a red dot (RMR) on the larger one. DIdn't affect function that I can tell. Was thinking about trying one on the compact. Had not heard what jjw's smith said about the slide being too light. Wondering if that was reference to slide having too little mass, or being too thin?