Use of android phone instead of dedicated scan gauge II

I use Torque with an old smartphone I had lying around doing nothing and a Bluetooth OBDII dongle. I just leave both hooked up in the vehicle when I am on trips. Once it is set up, it takes just a couple of seconds to turn on. Torque can display any information that the ECU can provide. The MPG calculation is pretty close for me (<= 5%), but you can adjust it to make it even closer. The dongle was about $25 and the app was $5.

I say go for it.