I honestly don't see any reason for using the slide stop, outside of locking the gun open. On reloads, make it a habit to use your support hand to grab the serrations with an overhand grip, pull the slide back slightly and release (make sure to never ride the slide).

Hell, even if i'm practicing support hand or primary hand only, I just use my belt and the rear site to close the slide on a reload. Another good habit in my opinion. I would be careful trying it at a stationary indoor range though... but those types of ranges arent good places to simulate an injury situation anyways.

If you have the ledged rear sight on your M&P, start testing it for reloads or malfunction clearance. Just be very concious of where the muzzle is pointing and make sure your finger is off the trigger. If you don't have a ledged rear sight.... maybe consider them if you are ever looking to replace the sights. There are a good amount of night sights that come ledged for single hand malfunction drills / reloads.

Steve