I am not sure where you got your information, but I have a Garmin RV model and I am happy with it. I think everyone will tell you that you cannot totally trust any GPS that you get. You need to check the route yourself to check for clearances. You can do that using a trucker road atlas or the web. I always check my route a number of ways.
Having said that, I would not go on a trip without the Garmin. It is very useful. I like that it tells me ahead of time if there is a curve or if there is a change in the speed limit. Both warnings give me time to slow down, if needed. I really like the large screen on the RV model.