There is some interesting information in this book to be certain, but ultimately MacInnes spends more time arguing against other theorists and not enough time developing his own thesis directly.
The argument that gender doesn't actually exist as something individuals possess is not an earth shattering or revolutionary idea, and it seems odd that he doesn't even give mention of Judith Butler and gender performance at any point. Not that Butler is without her own flaws, but it's sorta like writing a book about quantum physics without mentioning Einstein.
Ultimately I think MacInnes intends for this book to be more of a conversation starter rather than the final word on gender and sex, and thinking of it purely in these terms the author accomplishes what he sets out to do.