I have never used the bulk rimflex material but I have used the rimflex intake/exhaust gasket and it works really well. On one of my motors I run a really old set of clifford long tube headers. I probably purchased these headers in 81 or 82. They always warped a bit and always leaked. I would use muffler paste on the ends to help quell the leaks. Once I used the rim flex, nada. I was sold. I have used them on probably 10 motors so far and frankly would never go back to the original style gaskets.
That being said, there is one draw back. If you have to remove the intake/exhaust, the rim flex is a little messier to remove then the stock gaskets which generally just fall off. But that is part of why they work so well.
