I use the Garmin RV unit and it has been great. You build profiles inside the GPS and it plans your routes based on vehicle dimensions and driving preferences. I have three profiles in mine 1) Motorhome + Toad 2) Motorhome alone 3) Toad alone.
Since switching to this unit I have been far more comfortable on drives where I am in parts unknown. When I was towing a smaller rig I did not mind what my family referred to as "Our GPS Adventures", we got to see some parts of North America that we otherwise never would have travelled. Now with a Big Rig that I cannot reverse (without disconnecting the toad) I prefer avoiding the adventures that take me off the main routes.
With the Motorhome + toad profile turned on the Garmin GPS keeps me on the main highways, it knows bridge hieghts so no fear of sheering off my A/C and it knows my width so no narrow bridges to contend with. I also like that it gives me clear visuals of upcoming lane changes showing me exactly what lane to be in... I have found a few States where the local engineers were clearly into the Moonshine before they planned some of the highways and byways