Currently using the 165mm x 165mm (6.5" x 6.5") BuildTak board with PLA and have to say it’s one of the best things to print on. But be careful if you’re using it - you have to adjust your height REALLY exactly. If the extruder hits the plate just once you can throw it away.
Not sure if this has been addressed in the past 5 months since this announcement, but I also use BuildTak, but don’t have an Ultimaker, nor do I live in the UK. I’d absolutely love a discount, as I seem to go through sheets of the stuff a bit quicker than I should. I have a Lulzbot Taz 5 (300mm x 300mm bed) and live in the United States. Please extend this discount to other printers!