[Arragonis]

I think the additional cable is longer. The standard one is 6ft long so it routes fine in my car but I suppose if you wanted to do something fancy like a roof mount you might need something longer. Most people I seem to go for mounting on the bit just on top of the steering column in front of the main instruments, some go for the dash.

You could buy two if you wish to route the cable out of sight in two cars. That way you can just remove it by unplugging the SG end and then plug it back into the other car.

There are instructions (I think) on how to remember settings and calibration from one car when you temporarily use it in another.