I looked at these when I was driving professinally, but decided to just keep going with my Tom Tom VIA 1535. Works decent enough. I just plan for the fastest route when towing and it stays on larger roads. I don't need it most of the time until I get close to where I am going, and it if wants a different route, tough.
I was in North Beach picking up steel that needed to go to South Naples, figured I'd go across 41. Well it weaved me though down town Maimi, which didn't make me happy. It was the traffic that bothered me, which would have done the same if I was dead heading. I am always looking for signs and whatnot so I know where not to go and other possible routes. 27K pounds and 56' of truck and trailer on small side streets is managable, but its the traffic thats killer.
The thing with the RV and Commerical GPS is its supposed to watch for bridges and weight restrictions, but they can be wrong, and from the reviews I read, they're wrong a lot. So spend 4 times as much on one, and still have to rely on your common sense, yeah no thanks.