These are the same adapters you see at every growler fill station. Now you can show up with your own, and get them to fill your keg directly without ever being exposed to oxygen.
If you already have a Mini Keg and a Pro Tap Kit but you want to bring the freshness of your beer to the ultimate level, here is the way.
A regular growler will only keep beer fresh for a few days. The Pro Tap Kit will keep it fresh for weeks, which plenty for most people. But if you really want to make it last you need to make sure it never comes in contact with oxygen.