The Black Belt Club idea itself to me is not an issue it's how it's executed in some clubs. I've seen places where they're asking students after they receive their first belt if they want to join the "Black Belt Club" which you pay for in return can take an extra class or weapons training. In others, I've seen it happen when the students reach the advanced class, In this case I think it's OK, the intstructor is going to be commiting a lopt of extra time in preparing the student and having the affirmation that they are commited as well as covering the extra costs makes sense. At this point expectations and goals can get set, etc, etc.