I consider this excellent journalism in the spirit of muckraking journalism. The only link I followed was the one that led to the source that is selling one of the books by the author. As much as I enjoy this kind of book and would like to read it there are just not enough hours in the day to do so. So, as far as well sourced, I have to believe the author had access to the documents he cites. If you get so cynical that you eschew all claims of source then you might as well go live in a cave. Important? You bet it is! I firmly believe you have to read as many differenct sources as you can to develop a bigger picture of what is going on. It also keeps you from getting too far off on a tangent. I've seen evidence of this in conversations with others who only listen to one source, apparently.