I own a Smith & Wesson M&P CORE 9mm Ported Performance Center. The barrel flip is reduced and it shoots well. What I dislike is the front sight becomes covered with burnt powder residue after just a few shots.
I also own the standard M&P Shield which I like. I personally feel the standard Shield is the better deal for the money.
I'm a little bias because of issues I had with my higher priced CORE new out of the box. It came with a bad striker assembly requiring the CORE to go back to S&W. Yeah, they repaired it and it works, but no excuse for S&W lack of quality control.
My Shield worked the first time and has never failed to fire. I have many round of various types and all have worked perfectly. I know the porting looks like a cool feature, but I wouldn't pay extra based on what I now know from my own experience.