Things done well: Gender inclusivity, simple clear language, non-shamey discussion of things like leaking, inclusion of reusable products.
Things I wish had been included: a dimple diagram of a vulva, simple diagram of inside, uterus & fallopian tubes, a few more sentences on pregnancy. I know these are probably all left out because the book is a very focused look at periods and not a general puberty or sex-ed text, but it's still important to cover these topics at least a tiny bit.