Shortly glancing at a 3.5" screen - just off the steering wheel - to verify that I am where I think I am doesn't sound risky at all to me; I'm certainly checkin

Shortly glancing at a 3.5" screen - just off the steering wheel - to verify that I am where I think I am doesn't sound risky at all to me; I'm certainly checking several objects of this size (and further out of the road's direction) more often than I check the GPS anyway (rear-view mirrors, the speedometer, and the dashboard combined display, in decreasing order by frequency). Moreover, if you're doing 70 MPH, you're probably on a motorway - in that case, you should be prety well aware what's in front and behind you, at what relative speed, and how far. If all these are within a safe range, checking a nav unit shouldn't divert your attention for too long for any of these parameters to become unsafe, just like checking the estimated maximum range on the combined display. Of course, abandoning the driver's duties in congested traffic to play with a smartphone would be scary; but that's a different situation altogether.