Using Elm for an admin interface (not web-facing).

Elm is incredibly reliable (that's why we experimented with it in the first place) as well as very productive once you get used to the Functional paradigm.

Refactoring especially is a breathe (as long as it compiles, it usually works) and we didn't need to test the frontend for it to stay sane.

We even started covering more and more of our admin's old views with it and are on our way towards an SPA.