I've had good experience with them.

 

Are you talking about the clear coated ones?
If so, I've used them with o-rings on, turbo and blown drag week builds. No leaks at all, 1000-2000+whp.
We use allot of their un-coated ones on our alchohol/no water drag race stuff too. Seem to be good. They are made with very tight tolerances , so I've had to work a couple of dowl holes here and there.

 

The are called RCC Copper. Rubber coated copper core.

 

I use them in my 2500 hp blown TD BBC 30lbs boost. Orings in the heads, receiver grooves in the block. Wet block and heads and have not had any leaks. Also have re used them and sprayed with copper coat. Again no leaks

 

I have used them on several combinations with o rings. No water leaks. They work great.

 

Thanks for all the help!