From the blurbs, the book seems to be devoted to showing how Hitler and the Nazis "ruthlessly suppressed firearm ownership by disfavored groups," including Jews and leftists, as part of their consolidation of power.
The clear message seems to be: if the Nazis embraced "gun control," well then it must be bad.
The first objection is that the Nazis did not practice gun "control" but gun confiscation, which, needless to say, no one (with any shred of political realism) is suggesting be pursued in the U. S. Gun control in America is defined (tepidly) as gun registration, or the requirement of a waiting period before one purchases a gun, or the requirement of proving one's mental health, or a lack of a criminal record. Halbrook seems to be muddying the waters in describing the Nazis' policies as gun "control."
The second objection is counterfactual: Halbrook was asked in an interview if "allowing Jews to keep firearms would have made much of a difference in the end, given how well-armed the Nazi regime was. He replied by noting: “Had the Jews not been disarmed, they would have had a better chance to resist and survive, even if only in individual cases or in groups."
I suppose to best rejoinder would be that, yes, the Jews' ability to resist would have risen from next-to-impossible to barely-possible. To be sure, Jews were able to undertake limited resistance efforts in many parts of Europe during the war. But in Germany itself (which the book focuses on), the power of the Nazi state was unassailable -- and hardly only for potential Jewish resisters.
While the Gestapo and later the RSHA were not omnipotent, there were comparatively few opportunities for the kind of armed resistance that Halbrook seems to imply would have been possible had the Nazis never passed "gun control." A quick look at how the Nazis dealt with armed resistance groups in occupied Eastern Europe should put the lie to any notion that having guns will help you out much when facing a ruthless enemy waging a war of extermination.
Footnote: Any study that is described as "based on newly-discovered, secret documents from German archives" should immediately raise red flags for average readers. What is the definition of "secret," anyway? Does the presence of a document in an archive make it "secret?" Or is "secret" now just considered to be the opposite of "public?" Yet another sign of our inflation of language....