I installed the extension in MediaWiki 1.32 which seems to run fine, and so I tried a first user registration. The confidential email address is only visible on the access protected user accreditation page - as it should be. But here's the shocker: on that page the "real user" name is missing - instead it appears on the publicly accessible user page!
So, here's a request to fix it in the next update. Meanwhile I added a warning message in my wiki, but I would like to already fix it in the script somewhere. Perhaps I'll find it myself in the coming week, but suggestions are welcome!
My mistake: as administrator we can delete the "real name" on the form when creating the account.