i had one for awhile. pretty awesome product for it's size. i could scan codes and clear them, which was nice. also i could correct the speed for bigger tires/gears which helped, and use that to figure out fuel economy. also shows battery volts, and water temp and all that good stuff, really useful to make sure nothing calls it quits while you're on a trip. i sold it though, and bought an ultra gauge for about $60 after rebate.
bigger in height, narrower, and a lot thinner. it's a comparable product that gives an audible alarm for a warning code that pops up (happens a lot for me thanks to an O2 leak), but can't show a corrected speed like the scangauge. also, the mount on the ultra gauge kind of sucks IMO cus it's only a suction cup mount that they warn you how to handle cuz it breaks so much. but i prefer the darker screen of the ultra gauge especially at night. other than those things, i can't read battery volts like the SGII, or maybe i can and i haven't figured it out...
i've been happy with both though