I'm a fan of the Hornady Critical Defense. I've shot it into wetpack through multiple layers of denim, heavy cotton and even a phone book and it's always expanded picture perfect.
That day I also tried some of the 'classic' HP ammo (Speer and Ranger if I remember right), and in both cases I had at least one round that clogged up and turned into ball ammo. I never found those since they blew through all the wetpack and continued downrange, but that's the only thing that could explain their sudden ability to over-penetrate like that.
I would also think the poly-tip would help feeding, not hinder it.
I believe most of the concern with Critical defense / Critical Duty is that the polymer tips hinder cycling when hitting the feedramp - obviously, angles and tolerances vary; I'm no expert, did not stay at a Holiday Inn last night, but it would make sense to me that the polymer tip has more potential to slow the forward movement (a binding effect) - Think eraser on metal compared to brass on metal.