Read if you are a die hard for the series. There’s not a lot of new information presented. It kind of rehashes the things you already know about Four as an initiate, but you get to see them up close and personal from Four’s perspective. You also get to see more of Amar.
I am not sure I had to read it or that it added a lot to the series or the character development for me, but at the same time, I don’t mind that I read it. It didn’t thrill me by any means, but it was an easy read.