If I'm honest, I've not yet discovered hugely different features. My understanding is that kbin allows more integration with the non-threadiverse bits of the Fediverse (for example, Mastodon) than Lemmy, but so far I've not made use of that. Kbin is also newer and therefore seems a bit rougher around the edges, but that will pass.

What initially drew me to kbin was more not wanting to get dragged into the tankie noise around Lemmy, but as the number of instances have grown that seems to have become less of an issue.

What I will say for kbin though is that Ernest (the kbin developer, who also runs the kbin.social instance) seems quite nice and is very responsive and transparent with the community.