I always prefer to have a picture in my head of the overall route ... so I have a vague idea of where to head if I decide to divert away from something that appears to *me* to be dodgy. I'd love them to have a single button to press to swap between "big, overview map" and "small, detailed map" quickly.
But, otherwise, I am indeed a convert.
However, one aspect of the satnavs that I dislike is when they take small shortcuts off the main roads in order to shave a few microseconds off your journey. I had one example of this last week with a Garmin ... As the A1(M) southbound approaches the M25, to then turn west, the Garmin takes you off the A1 onto the A414 dual-carriageway at Hatfield, to join the M25 alongside the M1 junction. Instead of a benign run in motorway conditions, it chooses to dump me onto one of the nastiest rat-run dual carriageways ... with a sudden increase in stress, all for the sake of 2 minutes.
I could, of course, ignore the satnav under those circumstances, but you don't know if it has chosen that odd route as a consequence of traffic in the first place.
Satnav's have options for least time, least mileage, and best economy. Where's the "least stress" option? Though that would probably miss out the M25 altogether!