I used my Tom Tom one on a recent trip. I took a 129 mile loop because the Tom Tom told me to turn in the wrong place.  When I finally returned to my originaltion point, bought a map and passed the same turn, the second time, it did not tell me to turn at all! I do not think the device differentiates between the most commonly use routes and the most direct route. It seem to be most effective in the city areas, but I would not trust it in rural undeveloped areas. It lead me though the most uninhabitied oil fields in western Colorado. When I finally had me turn onto a dirt road in the middle of...