Fred-

I can tell you not from personal experience but know many that have them and LOVE them.

Jok is a racer, writes for his own website and columns and a previous track owner. So he understands what these are about and the reasons he developed them.

Everyone I know loves them, and there is only issues when backing up you need to take care of.

They talk about them often on DRR if you want to take a look over there. I do believe Jok even pays contingency on them for any race, not just certain ones.