Scangauge: Very versatile, has a lot of parameters, can use it to code stuff ie reduce Reverse Beep to 1, compact and most expansive Ultragauge, Bigger screen then SG, LCD Screen, fewest parameters of all, requires a mount and < $100 Torque App: size Dependent on what phone/tablet your going to use, custom parameters, requires mount, BT OBD II connection, price: app price, device price and $50+ for bluetooth OBD 2 transmitter, I have ultragauge, i bought back in 2011 and its been working just fine even in +100*F temperatures and subzero winters im sure the SG will hold up just fine too, I mainly monitor my RPM, ICE temp and a few other stuff.
I use ScanGauge-II because it is the first such device I found, and it provided the information I needed in a previous gas-guzzling car that lacked an mpg gauge. Its user interface is straight out of the 1970s, and off-shore copycats could produce knock-offs for a tiny fraction of the price. Fortunately, its value in that old car was so great that even at full retail, the SG-II paid for itself in about 7k miles when gas prices spiked in 2008. In a Prius with built-in mpg display, it will take far far longer to get payback in fuel alone, but the other features also have value to techies and gear-heads. Folks with smartphones (I don't) can get the Torque app and a Bluetooth dongle for considerably cheaper, and get a much nicer user interface. Besides Ultragauge, there are several other engine monitors competing in this market. DIYs familiar with Arduino can even built their own, the MPGuino.
Will the torque app shut the reverse beep off (1). That and ICE feedback would be nice, along with the ability to read codes.
