When I was primarily using Python, I didn't really "get" Mise. Uh, that's what we have uv for! But it really shines when using things like Node where you want a specific version in each directory, and also want common entrypoints like `mise build` or `mise test` in every repo, regardless of its language(s).
Don't get me wrong: I also adore Just as a task runner. It's what got me off of Make, which is incredibly powerful but somewhat lacking in the DevEx department to say the least. It's probably more "powerful" than Mise's tasks. However, Mise's combination of really good — not astounding, but really good — task runners plus all the tool management stuff is unbeatable for the things I work on.