There is no way the Discover pro is worth £1700. I have ordered the normal sat nave for £700 and that is a total rip off. (I use sat nav every time I use the car due to the nature of my job)
Exactly what do you get for an extra £1000, a slightly bigger screen and some features that you will never use.
Think of the computer you could buy for £1700, a top of the range TomTom is only £200.
Its almost a crazy as spending £1000 on an extra inch diameter on your wheels or some sparkle in your white paint.