No religious community is monolithic. Many people who consider themselves devout dissent from certain aspects of their religions. One cannot assume that because some sage wrote something thousands of years ago that modern adherents necessarily act on those passages.
The failure to make the above point clear, especially in light of two thousand years of anti-Semitic persecution, is a serious flaw in an otherwise good book. The reader unfamiliar with Judaism might erroneously conclude that all observant Jews agree with the more extreme passages cited by Shahak and Mezvinsky but, in fact, many do not.
The authors have done an excellent job dissecting one part of the spectrum that is Judaism. Yes, ther are observant Jews who are racist, discriminatory, and advocate violence. I was reminded of that when talking to a formerly secular friend who has become observant. He returned home from a West Bank Yeshiva and openly laughed about settlers who shot Arabs guilty only of quarrying stone for their houses.
Still, these fanatics do not represent all of Judaism.
On a personal note, I have met both Shahak and Mezvinsky. The world has never seen a finer human being than the late Israel Shahak. His years of suffering in the Warsaw Ghetto and Bergen Belsen left him with a deep sensitivity for the oppressed. He was a secular saint.
Mezvinsky is another person altogether, but I really can't comment.
I know little of Judaism and therefore must rely on the expertise of the writers to evaluate the book's worth. On that basis, the quality of the book must be uneven.
Mezvinsky was trained as a historian but his publication list is poor indeed. Most of his writing seems to be for popular magazines like the "Washington Report on Middle East Affairs." He has very few publications of a truly scholarly nature and many of those were collections of other people's work that he had edited. I have read a fair number of books written by scholars of the Middle East and can't remember a single one ever citing Mezvinsky's work.
There is nothing in Mezvinsky's list of publications that even remotely suggests that he has any expertise on Judaism as a religion.
Incidentally, years ago, Moshe Menuhin wrote a book entitled Jewish Critics of Zionism. In his book, he described Mezvinsky as a "clever but arrogant and presumptuous fellow."