I did a three month loop back East last Fall and depended on my Android phone with Google Maps at times. It was more than adequate for my purposes however it was doing one thing that drove me absolutely nuts.
When out on secondary roads coming up on a rural town with a cross intersection or perhaps a red light it would for some reason turn me off on Farm roads to go around those little towns which quite often got me into difficulties with narrow roads with no white lines where hopefully I didn't meet any other traffic.
Considering that you have tunnel vision when following a map on a phone you can't really see what's coming up ahead very easily so I started getting paranoid when it wanted me to do sudden turns off of a good road.
I think where full-blown good RV GPS might come in handy is in major cities where apparently they will line you up with what Lane to be in to to get through town. Since I spend practically zero time in cities and prefer to blow a day going around them I just don't need the full-featured GPS units.
Like a lot of things in the RV World it comes down to your style of travel and what you're comfortable with. For me I'll stick with the handheld phone.
95 Winnebago Vectra 34 (P30/454)