Number of financial companies using F# is about the same as for OCaml (but numbers are not evolving in the same manner). F# uses .NET which is way more tested than OCaml runtime. F# uses .NET libraries which are way more tested than OCaml libraries. F# core language is still a bit less tested, but considerable work is being done. In contrast, there is only fulltime person working on OCaml. OCaml community is dying, while .NET community is huge.