The poly ones are not very good. I run the fiberglass ones that JD/A&I has. They are stiffer and will feed in just like the steel ones. The poly ones tend to bend and not feed in correctly.
Also I found that if you are still using the steel fingers use the JD ones. They are harder and will break rather than bend. I also have took my cut off saw and cut the new fingers thinner at the break point.