It depends!
If your child is on the Books to Read Aloud stage, there is no need to subscribe to the Early Reader Club. As a Play Kits subscriber, you get the best deal by adding Book Bundles to your subscription. With the Book Bundles add-on, you get 2 additional books with every Play Kit for $9/book, and no additional shipping fees.
Most of the Play Kit books and Book Bundle books are included in The Early Reader Club. Play Kits subscribers can purchase the 12 books that are unique to the Early Reader Club (not included in The Play Kits or the Book Bundles) in the Subscriber Shop for $9/book.
If you're on the Reading Skill Set stage, you can access the Reading Skill Set materials either by subscribing to the Early Reader Club for bimonthly installments, or by purchasing a full Reading Skill Set box at once.