One caveat in regard to the power ON and power OFF capability when your vehicle's engine is started or shut down - even on TomTom models that support this feature, its availability will depend upon whether or not your vehicle has switched power to the cigarette lighter outlet(s).
Many older vehicles do not have this - for example my Ford and my wife's Lincoln have power to the lighter outlet at all times, regardless of whether or not the engine is running. On those cars the newer TomTom units will turn on as soon as they are plugged in, and will remain on while plugged in.
Many (but not all) newer cars, such as my son's Toyota Scion, have power to the lighter outlet connected to the ignition switch, and would turn on the TomTom only when the engine is running.
With best wishes,
- Tom -