I think the most efficient way of driving would be to keep the throttle at a set position, which means slowing down when going up hill, and then speeding up when going down hill.

Not sure why I say that, it's just a hunch.
 
Just looking at the Superchips site and the price is quoted at £435, anyone know of a way to get it cheaper?
 
Tried phoning them up and asking for a discount? I've tried it at a few places and you'd be surprised how many places it works at! :)