i have the tomtom go510 for my other car. Here are a list of thigns that the BMW GPS has that tomtom doesn't:
1. NO need for suction cup (the one that came with it, keeps on drooping. I ordered a replacement and its the same)
2. When you turn it off and on, it takes half a minute to find out where it is.
3. There is no way to filter search results (for example, in the BMW GPS, you can search a restaurant by type of food)

All in all, both have their strengths and weaknesses (BMW GPS sometimes freezes, etc.)