the accuracy issue is likely because of the nature of OBD. There is only so much resolution available over the obd port, and you don't really know what proprietary algorithms SG or kiwi use so cannot assess what lengths they went to to compensate for the lack of resolution of data over the obd port.
Here was the intro thread, I think someone needs to test the kiwi mpg in any event:
http://ecomodder.com/forum/showthrea...-mpg-6750.html
in the SG, though you can see a lot more vehicle parameters (coolant temp, air temp, etc) over the obd port, which is OBDs real strength. So it seem a shame to toss it out.