TomTom is compatable with Google maps. The new rider even comes with a programm to make your own routes - Tyre - and Tyre allows to import ANY route, made in Google Maps, or even Mapsource/Basecamp. As long as it is stored in *GPX format. The only difference... Tyre is sooo user friendly what you cant say from Mapsource.
Its funny... despite that TomTom has done a great job in solving the complains from the past (Tracklog function added, unlimited waypoints added, free live-long map updates) and still is the best (and fastest) SatNav for A-B navigation in Europe, the Garmin Boys still do their best to give it a real good bash...
I have been travelling around Europe and South Africa for decades (from which the last decade with the TomTom Rider 1, II, Urban and currently the Urban with IV update) also together with Garmin users and in a direct comparing, the TomTom does it good. Ask Jess. His Zumo tried to get him lost from Essex to Wales where my TomTom rider saved the day - not once, but on several occasions.
There is only one device which is better (with 3D!) and that's an Magellan GPS.
And sorry Stewart, but TomTom rider IV has won every direct comparing test after its introduction. Even in Germany, a country in which Garmin had a long history...
Maybe not in the good old UK... but you still drive on the wrong side, and use those silly measurements...