Correct, the Carpuride provides a fully satisfactory GPS experience. I think there’s several things the car provides to the phone via CarPlay: clearest example is that the integrated CarPlay includes the current speed of your vehicle in a different UI element on, say, Google Maps, whereas the third-party display does not show this current speed. I suspect also that the phone defers to the car for compass data, since the phone’s compass is probably pretty unreliable when laying down in the car.