All the features are opt-in. I started using mise because I wanted something like asdf only without the bad UX, and mise can use asdf plugins.

For env vars, you don't need to load them into your shell if you don't want to. When you run a task, mise will make sure the env vars in your config are set, so thats not something you need to worry about.

I still use shell scripts like you describe, mise just supercharges them a bit. When I need to make sure my teammates have the tools in that script (like jq) installed, mise just ensure they are installed before running the command, as long as you declare them in your tools list.

If your setup works for you thats great.