Terry, as Marvin states, an outside antenna/receiver will make the difference between being able to navigate and not being able to navigate in certain conditions and locations. Yes, the interruption in reception is temporary-and from experience this loss of signal lasts exactly long enough to make the wrong decision and one will always reacquire the signal in time to realize that you turned the wrong way. Oddly enough in our travels, the road ALWAYS turned into dirt just as communication with the system was re established. Not much of an issue with auto travel-but it will add a new level of adventure when driving an rv and pulling a trailer.
Is a Bluetooth system more portable, not really-neater? absolutely. If someone is concerned about attaching the antenna/receiver module to the vehicle you have the options of magnetic mounting or velcro. We have had the module velcro'd to the topcase on our motorcycle for approx 7 years with no issues at all, and the bike sees extensive off highway use.
It comes down to this, if you want a more reliable system you have to have an external antenna/receiver.
As to rf radiation, yes it is everywhere, but again, it is NOT good for you. And, with the earbud or with handheld phone use; you become part of the antenna system.
Having raised the issue I will say that, I did survive many years of using high powered portable radios, uhf vhf, 5+ watt power range AND more than a few minutes standing in close proximity to external vehicle antennas with relatively very high power radio's
(relatively speaking) with no known damage: but again-it ain't good for you.