Was it an option for your model??? ( Pig WRX I am guessing )
The one on my Pig STI is the best cruise I have ever had as far as keeping a stable speed. Every other one has been a bit like a rubber band. Think it is done direct through the
ECU ( could be wrong though ) would be the best way if it is.
If it was an option check with subaru cos it will be a much neater install if they can do it.