Lane guidance is very hit and miss. It often tells you to keep right on motorways and dual carriageways when what it actually means is don't turn left into the slip road.
They are good for getting you to your exact destination if you are unsure, but you are far better off knowing roughly where you are going and ignoring it if it tells you something stupid.
For that, I would say the cheapest TomTom is just as good as the most expensive. They all use the same software after all.