Hey, I just finished a game I made with kha for the xoxo game jam (you can check it out here: https://blazingmammothgames.itch.io/bun-snap).
There were a few pain points but overall I think using Kha in an actual project went quite well!
Made with Kha: Bun Snap
Even more fantastic because you shared source code - thank you!
Note here: it's good example how to use your collision library https://github.com/FuzzyWuzzie/headbutt
It's collision detection library only, there are no collision response, are there?