That's the new, official, Apple battery case for the iPhone 6. It's also a whole heap of ugly. Not that this will pacify the folks at Mophie, who's battery case has been completely ripped off here.
Apple is promising 25 hours of talk time with the new case so there will be some benefits to owning the worst looking iPhone in history.
No details on charging time or capacity, however it is available in both black and white and is made of soft silicon, so should be quick and easy to remove from your iPhone at the first available opportunity.
Treat it as an external battery pack which just happens to attach to your phone and it shouldn't be too unpleasant.