Cross-platform (Android/iOS and you can even build for desktop or web)
Has some neat features that I haven't seen in other clients, like a really customizable FAB, material you theming, multiple anonymous instances, ping time and version info for instances, already supports 0.19 including new features like instance blocking, an advanced share that can create a microblog style image to share posts
Very good accessibility
and lots more.
Coming from Relay for Reddit, I feel very at home in Thunder!