I read The Anxious Person's Guide to Non-Monogamy after having it on my book pile for years.
It's not wrong but it focuses a lot on people who want to open up an existing relationship. That's something I have never done so I can't speak to it much.
It does cover a lot of basics though.
There wasn't anything new in it for me, which after over a decade of practicing non-monogamy And reading a few other books before, isn't surprising.
My main criticism is that it doesn't actually talk about anxiety much, and the specific things a brain with chronic anxiety tends to do.
It's mainly general advice and just states that anxiety can make things more difficult. (Yeah, no shit)
It's also very much rooted in cognitive behaviorist psychology, and very symptom-oriented. It doesn't invite you to explore WHY you have certain complicated feelings, only how to handle them, and only on a quite superficial level.