My choir director gave me this book when I was sixteen, before I'd ever heard of the person profiled or most of the men she taught. It is an amazing read even if she did occasionally make stuff up.
It materially shaped my concept of what it means to be a musician and how we need to listen to a score for its ideas and not just for its stylistic alliances. If anyone has the right to tell us that, it's Boulanger, who taught everyone and their lover.