I have two Shield 2.0 pistols in 9mm. One has a safety and the other does not. I have always treated the slides as interchangeable - meaning that either slide could be used on either frame. I have never had any issues or malfunctions.
Recently, I was told by a gun shop owner that I should not put a slide that came on a non-safety frame onto a frame with a safety. He claimed the safety might not work as intended.
I've been shooting M&Ps since they came out and I have never heard this.
Can anyone comment on this?