Why dont you use it with your OBD2 car?
I have OBD2 car with factory computer and I am still using mpguino
It gives much more info and mpguino is accurate for measuring fuel economy. Factory computer is too optimistic.
edit: seems that you use ScanGauge now. Anyway - if you want to fool some sensors then mpguino is better for testing - it measures fuel use, not try to calculate it using sensor reading. ScanGauge can give you false readings if you manipulate/fool sensors (or sensor is just defective and gives false info) that it uses for mpg calcualtions.