I don't like pulling studs out of aluminum when i can help it, my mod quad head uses seals instead of o rings, and i think they seal better and my trininty head uses no seal at all.I had a pro design head and i sold it. I had a few leakage problems but the main reason i sold it is that the coolant doesn't flow properly through the head and cylinders. The way the head is designed it lets the coolant shoot straight through the head across the top of the domes and doesn't make the coolant go down and flow through the cylinders coolant passages, were as say for instance a NOSS head has defectors built into the head which makes this happen for ALOT better cooling, other heads out there also have done this. If you look at a factory yamaha head gasket it all so blocks of the right passages to make the coolant flow how it should.
This is my opinion after the reasearch i have done, and after the different people i have talked to, i know there are alot of people that like pro design heads but i do not.To each there own :cool: