IO540
you know I hate trailing wires as well but the cheaper PCAS runs of two self contained AA batteries and the whole unit is about the size of a big matchbox. It is hardly a nuisance on the glare shield. True, you do have to replace the batteries every four hours but that is not the end of the world.
The more expensive unit does require an external power source but if you will, replace the cigarette lighter connector with a BNC and wire a fused supply into the top of the panel - technically removable and not a risk in any event.