I use F# at work. Really love the language but the connection to the dotnet ecosystem is a curse as much as a blessing. Having to operate in a world of nulls and exceptions can reduce/nullify the amazing benefits of discriminated unions. Often you are back to relying on the due dilligence of other developers as a result.
I use a lot of rust in my spare time. The runtime guarantees it offers make other languages feel like a house of cards in comparison, including F#. I coincidentally picked up an ocaml book yesterday seeking a more 'robust' alternative to F#. Unfortunately it seems as though ocaml is even more niche than F# (I doubt I'll be working for jane street any time soon)