When I ordered my new A3, I added the SD card nav to the options list on a bit of a whim really. But now I'm wondering whether it will turn out to be an expensive (Â£500) white elephant, and if an off the peg sat nav for a quarter of the price would be a better bet. I haven't been given a build week yet, so there is still time to cancel it. (Currently, I don't own a sat nav of any sort). Views and suggestions welcome.