I would encourage everyone interested in this book, this subject and in modern Judaism in general to remember that 'conclusions' are based on current and past knowledge, not on future discoveries. Sarkel is still under water and will continue to be for the foreseeable future -- who knows what information it holds? People have been twisting the ideas and findings discussed in "The Thirteenth Tribe" and "The Jews of Khazaria" to promote hatred for Jews for quite some time. That's not the purpose of these works, as Arthur Koestler himself addressed at the end of "The Thirteenth Tribe."
I've also used the bibliography to further my own knowledge, although I have found that many of the sources are out-of-print.
I look forward to learning more about the Khazars, who they were and who they became -- for today, I highly recommend Brook's "The Jews of Khazaria." It is excellently written, a fascinating work and will open it's readers eyes to some lesser known history.
Savor it, but don't rush to judgement!
The controversy about Khazar Jews and their intermingle with Jews in Lithuania, Poland and Rumania is discussed at the conclusion of the book. First, the author describes other incidents when non-Jewish tribes converted and became "children of Moses". Examples are brought from the Avars and Cumans in Europe, Edmoites in the middle east, and the "Children of Moses" in Ethopia, sometimes known as the Falshas.) Then author then contends that it is quite possible that Khazar Jews, now disbursed amongst several nations, intermarried with "local" or "genuine" jews, most notably in Lithuania as well as in Poland.
The book is somewhat `academic' in its discussion, but very readable. The book boasts in using "archeological" finds in its discussion; in fact, it mentions only a few such finds. It further fails to include maps, documents and other images that would have made it more interesting and `real'. Nonetheless, the writing is not `heavy' and the organization is intuitive. Each chapter can be read separately and the footnotes are worth gleaning over. Although some maps appear at the end of chapter 2, and some tables appear at the ends of chapters 3, 4 and 7, they hardly help illustrate the rich history narrated within the chapters.
For genealogists who are interested in the controversial around the origins of dark-hair or red-hair jews in Lithuania and Poland, I recommend reading a couple of introductory chapters and then skimming through to the end. For history buffs, I recommend reading the whole book and perhaps use a map to aid in the reading as there are numerous references to battles, invasions and travel routes that would be much easier to understand with a map at hand.
This is not an intro-to-genealogy or a how-to-start-genealogy book. I found the subject of Khazaria and the Jewish diaspora, and the narrative in The Jews of Khazaria enriching and expanding my 15 years of family history work. Therefor, I mostly recommend this book for genealogists with at least 5 years experience, with some idea about the origins of the families that arrived from the Pale of Settlement; Of course, independently, the subject of the empire of Khazraia is a rich with history and glamour. I find that the narrative of Khazaria and its place in Jewish history well narrated by Brook.