bazza,
I don't think you need the rubber cush type. I don't think mine is then again I'm not a technical genius either
It is true however that it is the cheapest performance boost you will give your bike.
I put it off for ages until Don talked me into it. And he was right. It just gives so much more drive out of corners and really gets the power down to the road well.
It also aids low speed handling and standing starts.
Davem