Which vertical links bush material?

For track use.

The BMR vertical links with polyurethane bushing is approx $200, Derlin is approx $350 and spherical aluminium is approx $500.

Are the spherical links worth the $300 over the poly? The links themselves already look 3x as thick as the factory ones.

For anyone who has done this upgrade which bushing option did you use? How much difference did it make?