I've always used the slide release but in a recent class we were instructed to use an over handed slingshot method for 2 reasons.
1. Muscle memory, helps with clearing a malfunction if that's the only way you do it.
2. Gross motor skills might be all you have in a stressful situation. Leading back to muscle memory, grabbing the slide with your off hand and pushing the pistol forward with your strong hand.
As for the 2.0 M&P's, the slide release does break in or you can work on the detent they added to stop auto forwarding when inserting a magazine. Personally, I liked it when all I had to think about was slamming a mag in and pulling the trigger.
