This book is basically a collection of interviews with various drivers and sometimes their wives, track managers, etc. that weren't included in the film by the same title. The author provides an exact version of each interview usually without editorial comment or polish which frequently makes for a disjointed discourse. He acknowledges this in the introduction and makes some apology for how it might appear to readers, but elects to leave the interviews complete word for word for the sake of authenticity and accuracy.
I suspect these interviews might have had more impact in the film, but I found the wandering commentary in prose less interesting. The focus is meant to be on the dangers associated with racing in this period, but the dialog often covers other aspects of Grand Prix racing that have little to do with the associated dangers. On the plus side, the writing style does give some hints about the personalities of well-known people from that period, however, it doesn't really convey much detail about the causes or what happened in many of the deadly events from that period other than frequent commentary that "racing was simply dangerous."
I did see the film some time ago and am personally inclined to think the film alone was adequate without having the book to accompany it.