> How much effort does it take to set up, though?

Practically none. And any designer is prone to reuse the same spacings from project to project. So you bring the language file with you. Something like this :

:root { --spacing-sm: 1rem; --spacing-md: 2rem; --size-tall: 32px; ... }

And you can do some pretty nice things with these pure CSS tokens. Without any hassle or dependency.