Firstly, this item is just a key to enable the Windows 8 **PRO** features for people (like me) who have the standard (non-Pro) version of Windows 8 - likelyhood is you bought a new PC and it came with standard Windows 8 already installed. If you need the Pro features such as Hyper-V, encryption, recieve remote desktop connections, need to connect to a Windows domain and Media Centre then this is a low cost way to get you upgraded. Certainly better value than buying directly from Microsoft who advertise a price of £99!
If you have an earlier version of Windows (7, Vista, XP) then you need to look at a full version (or full upgrade version) of Windows 8 / Pro, not this, as this product requires Windows 8 Standard to already be installed on your PC, hence the much cheaper price.
Secondly, shame about all the negative Windows 8 comments against this product - not helpful. If you are here to get the Pro upgrade you already have Windows 8 and don't want to read reviews that are focusing on some peoples dislike of change/new Windows/Metro or what ever they choose to moan about. Thankfully there are two or three real reviews for this upgrade product. As most people find with Windows 8, once you learn what's new and different, you will more than likely appreciate the productivity benefits and improvements and won't ever look back on the older versions of Windows.