The only thing that I've noticed over the years of lower durometer urethane is that when hot and high humidity, it gets REALLY soft like modeling clay. Now this take a couple years to happen, but I've had urethane .25" sheet in some storage drawers at home and when I took them out they were all sticky and soft.
I'm no expert and I would guess there are some mixes that won't degrade like the softer stuff I've seen.
The urethane that we use has little shrink, but it's 90d hardness. WAY TOO HARD for the use here. It does seem to be holding up over the years though.
Cast, once designed, would be simple and cheaper, but I'm not sure that I would say that I have a perfect mix when I pour, but good enough for my use. Also a 3-gallon mix that we use is almost $800. I just thought that if you bought a sheet from a manufacturer that you would be pretty much guaranteed of a consistent repeatable end product.
It will be interesting to see if the more of the rubber ones fail. I would think that "some" strategic cooling holes in the adapter housing could help dissipate some of the heat build up.
