I looked at it super-briefly. Honestly, I tend to prefer the kbin "I have a vision for what I want this to be and I don't want democratically inspired changes to my codebase" system over the mbin "if it looks good we'll merge it" system. Based on my little bit of experience with it, the backend of kbin seems relatively well-organized, and obviously he put it together well enough for it to be able to work in production on a busy site, so I trust his judgement a little. I didn't look in detail enough to make a real informed decision about it though. I do have some nitpicks with kbin (definitely as far as the frontend in particular) but relative to other Fediverse software it seems above average (although, that's a low bar.)

Looking over mbin now, the one thing that seems like a serious point in its favor is talking about security fixes. Do you know anything more about that? Are there security things that the maintainer(s) of kbin are not wanting to address or something?

Edit: Oh, also, update: It looks to me like lemmy.world is currently configured to break all incoming federation from default-configured kbin instances. Maybe I am wrong about that, but that's how it looks to me right now. I posted about it.