Sir, its a good gadget to keep an eye out on your fuel consumption. The display is eye soothing indeed. Nice choice!!
But I would like to highlight here two things (with your generous permission ofcourse).
Some vehicles provide the instantaneous fuel consumption directly on OBD2. The calculation is programmed inside ECU based on injector firing duty cycle.
Like wise, some vehicles donot support this PID. In this case, the external tool or gauge has to calculate on-the-go based on engine RPM and MAF values. You just need to enter the engine displacement. Its more of theoretical calculation
Example, ScanXL Pro that I use sometimes, calculates based on this method. It puts the engine CC, rpm, MAF reading in an equation and calulates the MPG or L/100km
Secondly, some vehicles do not support fuel level info on OBD. Only the instrument cluster works independently (though still communicating with ECU for Speed, RPM, DTC and all) and monitors fuel level, calculates distance remaining based on available level without telling the ECU.
That being said, I am positive and Looking forward to your installation, application and MPG accuracy in your case.