the scangauge is in my wife's altima now. i've found that the cortex is good enough for data logging. i also found that the SG mpg calc is pretty close to the oem mpg calc too. also the cortex has maf air flow which the SG does not have.
Also, adding the o2 sensor bank data to the SG is a royal pita. The cortex makes it super easy. see pics below
only thing is the cortex background light is white, while the SG has a rainbow of colors. but i like the bigger screen.
The Cortex can also track MPH (more pics!)
Here are the O2 sensor bank selections you can make: