I switched from vim+Merlin to neovim+ocaml-lsp and it is basically the same with a bit less hairy setup and overall it works rather well. I mostly only switched because my editor has native LSP integration and I wanted to try it and it worked well enough. It also has the advantage of working like any other LSP as well, thus I can use the same plugins that other people use to interact with their code with OCaml via the LSP interface which is neat.
The only thing I’ve used with Merlin directly that I don’t have at the moment is determining the type of a selection but honestly that was more of a cute feature than a useful one.
After all LSP uses Merlin anyway, so the results are about identical.