At the risk of jumping into a holy-war, isn't a polymer gun is more susceptible to limp-wristing, in general, than a metal framed gun, due to the lower mass and to a lesser degree, frame flex?
Having said that, my wife has managed to get a few stovepipes with my G19 (fixed by a better grip), but never on her M&P9c.
Edit to add: Yes, I think it's a grossly overused excuse for what are often really mechanical issues.
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As to the safety question, there's an optional lock (internal disconnect?), and also an optional mag safety.
My wife's has the mag safety, but not the lock. With the mag safety, you can pull the trigger without the magazine inserted, but it does not engage the trigger bar so the gun will not fire. You can get them with or without that 'feature'. There's apparently a way to disable this safety, which I'm pretty sure is on S&W's website. I can see why someone might not want this safety, but it doesn't seem to be a big deal, personally.