On two recent trips I decided to use TomTom for iPhone instead of my standard TomTom and very stupidly I left my my standard unit at home.
Driving around Edinburgh it was losing GPS signal, putting me on roads no where near I was and lagging so badly behind that it was really difficult to take the right turnings when they were really close together. We resorted to using Google Maps to route ourselves to our destination.
Obviously the limitation is with the iPhone rather than with TomTom hence them saying you need to have the car kit WHICH YOU CANNOT BUY YET!
Really wish I had not bought this, I feel ripped off and will be firing off an email to them as they simply should not have released this without the car kit.