It's still incredibly expensive using it in Caithness, even with the discount. As far as I could work out when I last tried to use mine, they calculate the discount on the full fare, so it would actually have been cheaper to book normally and get the discount for booking in advance. Wick's still an hour away for me, and I can only fly to Aberdeen or Edinburgh from there, so it's easier for me to drive 2.5 hours to Inverness and fly straight to London or Bristol.