FTF's likely due to grip pressure being exerted on the extended magazine. It can happen with or without the X-grip. I talked with Glock inc. about it and they confirmed that if you really squeeze hard with the pinky on an extended mag, it can cause malfunctions. The X-grip doesn't provide the stabilization to prevent it. I now pretty much avoid using larger mags in my glock 26 for defense purposes. It's easy to say just don't apply heavy pressure on the mag with the pinky, but in a life and death defense scenario, I imagine most of us will gripping our weapon extremely tight. I would think the same issues would apply to the M&P.