I don't have a Tom Tom. But, I just got a car with a navigation system built in, picked it up in Utah & drove back to Massachusetts. It was a great convenience - especially navigating to the hotels. (N.B. The database in the system was not a complete set of the entire US - so I had to call and get either an address near the hotel the system recognized, or actual - shudder - directions from a known spot). It also gave my son something to play with during the drive.
It was also useful on the major highways, because we did not take a direct route, but detoured for some sightseeing.
Overall, a really nice convenience. Potentially distracting while driving (there's always the urge to fiddle). And, it was still necessary to carry maps for overall planning.