Other then guaranteed spread of the hallow point, I really would not know... I have heard rumors hear and there that the poly tips are less accurate then an open tip (Nosler tip). Such as what’s found in Sierra match bullets. But I am not sure if that is true or not, I would have to see some testing on both rounds that can be compared. The basic complaints I have heard is that the synthetic tip can not be made to sit with in a thousands of true. Meaning the tip is not centered on the bullet. Where’s the open tip has a pocket of air in front of the bullet, that keeps the bullet true in flight (some kind of rocket doctor shit). But that’s what I have understood to be the issues of dislike by some people in the competition side of shooting.
As for the bullet expanding properly, I think its obvious that creating a small air pocket with in the core of the hollow point, that is pressurized by a synthetic piece pushing (on impact) into the air pocket’s hollow point will cause better expansion, then when it is a simple open tipped hollow point.
This would bring the old argument in to the loop again, “what is your preference” do you want accuracy or transfer of kinetic energy and are you willing to lack in one to have the otther.
Like I said I would have to see some testing on the accuracy effects between the two types of bullets. Being that I am more accuracy driven then expansion/ energy transfer orientated. I personally want to be able to be more precise in my shot, then lose accuracy to facilitate bullet energy transfer into the target.