I like the setting piece that this gives you when it comes to running Masks. It doesn't cover all of the possible playbooks, but it does cover the basic ones: and the history of Serendipity gives the GM a lot to work with when it comes to picking what elements are going to stand out at your table. 

If anything, I'd like to see more advice about translating MASKS to a magical girl setting: this was a good start but the itch is still there.