Relay has this feature for Reddit. In a thread, if you tap the comment icon on top all the comments will be collapsed except the top level ones. I personally use this on pretty much every single thread. It makes scrolling through a thread much less cluttered and its reads a lot nicer.
I also like that there if you collapse a comment thread, the top comment stays visible. Here it is hidden which doesn't add too much value in my opinion. As long as all the child comments are collapsed the top one could stay visible imo.
Other than that I really like the app so far. Keep up the good work!
Edit: btw I said button but if there would be some other way to do it that would also work.