Just seen a bit of this on todays Apple Keynote. A launch offer with 30% off. And it's just up on the App store today. Affinity Photo for iPad supports iPad Pro, iPad Air 2 and iPad (early 2017). Please note that older iPads are not supported.
Couldn't find a youtube video but here's a link to the keynote. Can watch it in action from 100:15 https://www.apple.com/apple-events/june-2017/