That product has 98g of carbs per 100g which means, as I understand it, that it's not resistant potato starch but cooked potato flour (the terms don't seem to be used very precisely in the food industry). The one you're looking for has 80g carbs per 100g.
If you can find one via Goodness Direct, they also stock tiger nuts, which everyone has been raving about on Free the Animal:
http://www.goodnessdirect.co.uk/cgi...l/196963_Goodness_Tiger_Nuts_Peeled_250g.html