but this kata does both directions (number -> roman numerals and roman numerals -> number), while the other one doesn't

The F# version of this kata also seems to be broken - the sample tests work fine, but the "attempt" tests throw errors with (hopefully) correct as well as placeholder implementations. The errors thrown reference line numbers that don't exist in the solution code, and complains about "Dictionary" not being in scope, even though the solution code doesn't reference "Dictionary".

just a tiny nitpick - in the 'solution setup' section, both args are named 'words'