Figured I would throw my experience in here.
I have a PF9 that I got back in July(new). I think it is fairly new build.
It has had maybe 500 rounds through it, with not a single hiccup. It has eaten every type of ammo I've fed it, and I have no issues with carrying it.;
The only time it didn't fire was when I handed it to my father. He pulled the trigger back and nothing happened. Turned out he didnt expect the long trigger pull, and hadn't pulled it back more than 2/3ds of the way. If it wasn't for the LONG trigger, I would not think about any other ccw pistol. As it is, S&W Shield is where I will be putting my future money, but I will keep the PF9 (partially because it has crap resale value)
I think Kel Tec has gotten better about the QC of their guns. As a whole, the company makes some awesome products. Just seems they are too small to keep up with demand, and release some items before they should.
To OP, if sent in a gun with a broken slide I would be furious to get what you got back, I would be done too.