I use my Rand because of the huge screen...we can set it on the MH's dash and both of us can see/read it at the same time. It can hold a virtually unlimited number of custom maps, POI files and trips. When the cell rings, it doesn't affect that standalone unit at all... Uses zip, nada data from my plan. I can plan trips using the GS Trip Planner and download them to the Rand unit. I can't accidentally wash the Rand unit, leave it laying in a restaurant or drop it on the ground (it stays safely in its mounting unit unless I'm hooking it up to the computer to download new updates or trips and then it is two steps from the dash to the computer desk...
That isn't to say that I don't have or use NAV apps on our phones when we are out and about, but, for the "heavy duty" guidance of our motorhome, we rely on our Rand unit in conjunction with the in-dash built in that came with the coach. If both agree on the route we are confident...if they disagree, we start investigating the "why". Much the same as "two heads are better than none". We tend to treat our phones as phones. The other "uses" are neat, but, a standalone dedicated unit will always trump a smaller multifaceted device; I'm the same with my computer equipment...I have printer, I have a scanner, I have a separate photo printer, etc. A machine designed and built for a specific purpose will usually perform that purpose better than one that can do it, but, wasn't really designed for it. I have a "level" app, but, when I want to build something, I still use my 6' contractor's level to get it right...