As mentioned previously, this is a free preview of the app. Soon it will only be available to users who are part of NovelRank Pro, an upcoming value-add service that provides improvements to NovelRank that give your books priority as well as save you time and effort to get the data you want, all in a single annual fee for your entire user account. Until that is released, the web-app will stay free for everyone to use.
Let me know what you think of the app in the comments below!