I have a SuperPID waiting to be installed, but have not done so yet as there were other problems with the machine, they have now been sorted.
The SuperPID uses an optical sensor mounted in the case of the router. There is room as the existing speed control is removed. This means that the spindle must always be used with the superPID as otherwise all nasty things will happen, like overspeed and burn-out.

Have a look through the website http://www.vhipe.com/product-private/SuperPID-Home.htm

Hope this answers your question.

Cheers

Rob