Remarkably poor. Very light on evidence, repetitiously high on speculation. Sets out to prove a very dated thesis by hyperbole. I would recommend reading a proper biography of Eileen and I'm sorry about Ms Funder's dissatisfaction with her life but she could do something about it not write a book.
It is curious but perhaps revealing that my edition of Wifedom (Penguin 2023) does not include a single full face portrait of Eileen O'Shaughnessy (Eileen Orwell). We quite literally have no idea what she looked like. On the other hand we have a beautiful colour photograph of Anna Funder as a poised princess of literature. Freud said there were no such things as accidents.