I want to say I like this app before we get started. Sure, it's an unwise way to blow $4.99 on the app store, but would you really want to pay 4 times the price? I didn't think so.
The hub is Hogwarts or some sort of generic room. Seriously, I'm having a hard time deciding what this is. It looks like Hogwarts but not exactly like it. They could've expanded the hub but you wouldn't expect an entire world in 500 MB.
The Dueling Club is an extra feature you can purchase if you want to, I didn't. I just replay The Dueling Lesson level in The Order of the Phoenix.
Inside the levels as soon as you complete the tasks are blue 4x4 plates to stand on to go to the next level.