AFter playing with the S-AFC II some, I definitely liek the first one better. The S-AFC has amore intuitive interface and is much easier to use because of its push buttons versus that dial. It also has monitors for o2 sensors, and can do decel., hi, and low correctiosn as well as you ahve the ability to set the mesh points. It only has 8 RPM settings vs 12 and no knock sensor, but I woudl personalyl rather have the S-AFC and since you already ahve one, just keep it.