They do work the same, but the car GPS is far better for driving than a field GPS, in most cases. My brother uses his Rino for both. I have a Garmin c330 for the truck, and a DeLorme PN-20 for the field. The PN-20 can be used for driving also, but the screen is smaller and it doesn't track as fast. I love it for the field, because I can also upload USGS, satellite, and aerial maps. It's not limited to the topo software, which is lacking in detail.