I have seen a Glock 21 come apart at our range. The guy was lucky and only needed about 6 stitches in his hand where the slide stop cut him. I have never felt comfortable with ANY Plastic guns. When they do come apart, they really destruct, while steel and stainless steel seem to hold together better when they have a KABOOM!
I know fiber composites seem to have strength advantages over all of the metals, but I still can't be comfortable with them. I have shot most of the plastic guns at one time or another helping people with problems, but I try not to, unless it is impossible to avoid. I DON'T DO PLASTIC GUNS! I have never even had the urge to own one, and I am comfortable with that.
At my retirement company, with our tracked vehicles, we had tried all sorts of Composite structures, and there are parts of the suspension mounting, engine and transmission mounting, turret rings, etc, that always had problems. It never was good at dealing with certain chemicals or vibration, even when insulated from the vibration, mounting bolts would not hold after a short period of time. Composites and composites of composites make wonderful armor that works, but it doesn't take multiple strikes very well without losing most of its armor capabilities.