The only thing I know of that MSII provides and Extra MSI does not is
GM idle air control (stepper IAC)
Extra MSI only does FORD pulse width modulation idle control.
It would be nice to have the stepper control, but I want NOS injector staging, water injection control, and knock detection that the Extra MSI provides for my current projects.
Thats right, I said NOS, might as well play with everything