They are junk.. lasted me a couple months and slipped the outer ring... Same with the non SFI professional products, except the non sfi actually came apart.
ATI balancers are awesome, but expensive
Fluidampr Expensive, but awesome
Right now I have a trickflow Trackmax SFI Balancer, engine is still new but so far it's ok. We'll see how it does come racing season.
