It uses regexes to define the non-standard transformations and therefore doesn't provide much safety. If you need to provide the same pluralization and singularization which rails does out of the box, this will work the same. If you want more you should be using inflections-hs which uses megaparsec to give you more guarantees
In the description of countable-inflections:
The other library which is being refered to seems a lot better maintained as well https://github.com/stackbuilders/inflections-hs