I use nix-shell for dev environments. Once I've got it working it's wonderful - full replicable, across multiple development machines and CI. It's painful though. Some problems I've encountered recently on different projects:

Old version of fwup packaged. Can override to get newer version, but needed to add another dependency to make tests pass (and it gets built locally rather than being cached)

Pain getting my environment to include the right Python packages so I can run the gigalixir command line tool.

Have to workaround an oddity to do with how Erlang is packaged so that I don't get lots of warnings when anything is compiled:

    shellHook =
    ''
      export ERL_LIBS=""
    '';