You can get the extra discount via their Facebook voucher code, which you can find via the widget at the top of their store page. This isn't the first and definitely won't be the last CDKeys Xbox Live Gold deal we've run, but they've now dropped their price from £25.12 to £22.79, which is incredibly cheap Xbox Live deal indeed.
Despite a couple of shortlived recent hiccups, Xbox Live Gold is a price we're more than happy to pay for a robust online service, weekly discounts and monthly Games With Gold. Especially at a saving. Thanks again FantasyDeals!