It's a neat little language. The benefits are real when coming from JS, but not that special when you consider other languages. Basically everything said in favour of Elm is completely true, but it's not the whole story.

The ecosystem offers some trivial packages, but the hard stuff is missing. JS interop is intentionally quite painful. I'd consider it sufficient for fairly trivial SPA use, but lacking for anything large or anything requiring browser APIs.

The language development is a big red flag: virtually all commits have been made by a single developer. There are no RFCs, and the future direction of the language is very unclear. Any discussions about potential improvements are immediately killed. Releases are infrequent, and may cause very significant breakage, depending on your application.

It's probably the best thing in the JS ecosystem in a long time and i really want it to succeed and to use it more, but the current state isn't that great. Maybe in a year or ten.