> once you grab it, you can hold onto it during adjustment, even in a moving car
Unless they have a ton of resistance (old school cable actuated HVAC) or are massive (typical Honda HVAC) rotary knobs suck for adjustment when moving. You want discrete up/down buttons (preferably ones that feel different) and enough dead space around them that the user has something to touch to anchor their hand. We've all sent the volume flying on a radio with a knob.