ran it, its worth it. he also sells cust 12.5:1 pistons for the kits as well. AZ quad parts Matt is a good guy, I bought a ton of stuff from him. If you do run the kit toss the junk athena gasket and run a cometic. I blew the head gasket rather quickly running the gaskets they supply. Also do heavy duty head studs, a better water pump and porting. Further, when I had this kit 2 valves got destroyed cause the timing jumped. You are pushing a bit more engine that these motors are designed for. We narrowed it down to the automatic timing tensioner. Upon rebuild and a 470 kit we did a manual tensioner.
I have 2 other friends with the same kit running the 12.5:1 piston and no issues. Just make sure you port the head or you wont get the power it can really put out.