I read the O’Reilly book a few years ago. Kennedy’s Last Days is standard narrative and does not present any rebuttal to the mainstream “lone gunman” theory. I have to say it is beautifully printed: quality paper, hi-def photos, attractive layout with well-spaced type that is easy on the eyes, but it is written at a 6th-grade level. It’s a good intro to the (discredited) Warren Report narrative for middle or high-schoolers.
I am partway through the Prouty book. It is far more dense and focuses on background details in the years leading up to JFK’s assassination. It has a foreword by Oliver Stone which is very thought-provoking. Prouty was involved in decision-making for the Vietnam War and he knows the subject well. He offers a very different take on it than Bill O, who probably had his ghost-writer package info from the internet for him.
I challenge you to read them both and then tell me where YOU think U.S. tax dollars go after they skim off billions for the spooks at Langley VA.