If you are a huge fan of the Blood and Ash/ Flesh and Fire universe - this is absolutely for you. It's full of fun tidbits, helpful references and even a few original short stories from Miss Willa (she does essentially narrate this book after all!) It also has lots of art and other fun things that I don't want to spoil. This is so helpful for keeping everything straight, as the stories progress! As a massive Blood and Ash fan - I absolutely loved this. I wish more fantasy universes did beautiful unique compendiums like this!

If you aren't a huge FBAA/ FAF fan, you could skip it and not miss out on anything critical. That being said, while it may not be absolutely necessary reading, it will be a super fun and helpful way to revisit both series before the next books come out, so I'd still recommend checking it out if you plan to continue with the series!