That's not entirely correct. Any interface where you share your posting key can take part of your author rewards as well. The active key is only required to simplify the use of the multi-account feature and improve security, as is discussed in our post.
On the other hand, yes, we do charge a small fee for posting but it's only a 5% for posts and 10% for comments. Besides this you can try exploring our app as all other features are free.