So I used both a real Tom Tom One and an iPhone with Tom Tom US on it.
- The iPhone got really hot and the battery lasted just over an hour so it had to be plugged in.
I used a Griffin adaptor and the iPhone complained the device was not made for the iPhone and wanted to turn off the cellphone side to prevent interference.
If you said "yes" then it killed the GPS as well.
- Playing music through the iPhone while running the Tom Tom app was annoying as it dimmed the music for every direction. Maybe there is a dim setting somewhere but it was too slow a fade back up.
Navigation wise they both perform brilliantly.
But you can't beat the real TomTom if you have one!
Music up loud on the radio, voice up loud on the Tom Tom.