The battery itself charges the fastest with a 27W MacBook-style charger, but it also works with regular wall chargers. You can charge both the charger and your phone at the same time, which is handy when you’re short on time. Interestingly, it can also be charged in reverse, which means you can use your phone to charge the battery.
The MagSafe Battery Pack is (so far) only available in white, but in real Apple style, it looks first-class with its smooth rounded corners. It also comes at a premium price. For £ 99 in the Apple Store, if you order one now, it should be there by the end of July.
However, you need to buy the USB-C power adapter and the USB-C to Lightning charging cable separately.