Good to know: My screenshot was from the web version of the app store page (see link in my first post), the iOS-version shows month or year as you said.

The premium yearly subscription has 3 price points shown (22.99, 34.99 and 44.99€) - I feel really bad for the developer as their customers are reminded that they have to pay more than others have paid before. I don't get why Apple is showing the old prices.