Unlike the run of the Khazarian Jew hypothesis enthusiasts, the author does not latch on to every dubious claim; indeed, he repudiates many of them, including the work of the dilettante polemicist Arthur Koestler.
The author has pored over the available scholarship in many languages, so the reader is given a sense of what writing is out there and a sense of the progress being made in this field, however meager this is.
The author explains that the cultures of the Russian Steppes, the hordes who rushed west from Central Asia indeed had civilizations as attested by rich material culture left behind.
The author gives the standard argument for the existence of a Jewish dynasty ruling Khazaria -- rulers' names, travelers' stories -- , but they don't add up to a mass conversion, or even a conversion to Judaism as such. Traveler's tales are probably unreliable, since they could well be a matter of wishful thinking or a desire to impress an audience.
The author is not a scholar. He disappointed me with unsubstantiated statements such as most Ukrainian Jews had Khazar background. Most surprisingly, he doesn't even touch the genetic research on the matter.
The author's strongest point is that many if not most modern Jews are not descendants of the tribes of Israel and that this fact should be embraced.
I came away from reading the book feeling that I had a general sense of the Khazar hypothesis. I think it is worth reading -- with caution.