I purchased a W10 Pro key. I followed the supplied instructions, but they didn't work. They would work if upgrading from an earlier version of Windows, but as I already had W10 Home they only resulted in reinstalling it. I raised a support ticket - no response (2 days and counting at time of writing). I managed to find the solution myself online - a different upgrade method is needed when using an OEM key (which this obviously was) to upgrade from Home to Pro. So, 5 stars for the great price for the key, 1 star for the incorrect instructions and lack of support.