Everything about the story of William Patrick Hitler was fascinating to read, especially to someone who before had never even heard that Adolf Hitler had family in England/the USA. Regarding his story the author gathered a lot of information from diary's, interviews, news articles and even declassified FBI reports. Because he was such a public figure, I have no complaints about this.
Regarding the sons of William Patrick Hitler, who are still alive today, I have mixed feelings about the information published in this book. The author reached out to them multiple times, and they made it very clear that they wanted to be left alone. Despite that, the author kept trying and trying. He also published high school photos of them, and everything about their personal lives that he could find. Even seems to be revealing to one of Howard Hitler's (who passed away) friends that he was a relative of Hitler, which can be seen as controversial.
Even though I liked this book, I think the author could have respected the wishes of the remaining Hitler family in the US by keeping the focus on William Patrick Hitler, without bothering his sons. This story alone is fascinating already. And for the remaining family, being a Hitler relative is enough of a burden in itself.