Hi Ben,
To get “Pie Register – Post Restriction” to work, you need to choose your desired option from “Visibility” dropdown and type in “Block content”. Say for example you chose “Show to Non-logged in users” in the visibility drop down and in the block content you entered the message “You must be logged in to access this content”. Now in this case a non-logged in user will see “You must be logged in to access this content” while the logged in users will see the actual post you added at the top of the page.
Hope this helps.
Thanks,
Kirmani