I know nothing about the author and most of his subjects but I suspect he is probably pretty accurate in his description of the lost souls who gathered there, with one exception.
I disagree with his assessment of Lavoy Finicum as a broke rancher struggling to feed his 11 children and taking desperate measures to do so.
Lavoy and Jeanette do indeed have 11 children but only 3 remain living on the ranch. The other 8 are married with households and children of their own. All 11 of his children spoke at his funeral and quite eloquently, as well as Jeanette, his two younger brothers and others. He was remembered as a loving father and every one of his children admired and respected him. He started every morning with personal prayer and scripture study. Each morning and evening, he led the entire family in prayer. He enjoyed playing card games, board games and made up games with his children when they were young. One of his daughters recounted how he taught all of his children to ride and rope, to tend cattle, to handle and shoot firearms safely, and how to hunt, even his daughters. She also said he taught them how to defend themselves if necessary. Another daughter said he told them many times when they were growing up that of all the characters in the bible, he most identified with Job. Not because Lavoy thought he was a great prophet or that he had great patience or he was a man of great faith or that he had endured great trials. He most identified with Job because his daughters were the fairest in the land. One of his sons said he taught him how to be a good husband and father, and how to respect women and his fellow man, and he did this by example. Another of his children talked about how he would help his neighbors at the drop of a hat and recounted how after a long day on the ranch, a neighbor lady called seeking help with a load of hay. Lavoy left the dinner table and worked until after midnight unloading the hay for her. One of his brothers talked of what an inspiration he was and how he encouraged his siblings to attend church and live by Gospel principals. He said a turning point in his life came when Lavoy insisted he attend the Priesthood session of General Conference and took him there. His other brother described how Lavoy would stand up for his brothers and other kids when they were being bullied in school by stepping between the bully and the victim saying "If you want to pick on someone, pick on me". I was most impressed by how his children in their hour of grief could stand before 1,000 or so people, many of them strangers, and speak so eloquently from their hearts about their father without notes, then declare the Gospel for all present to hear and testify of their unshaken faith in their Redeemer, Jesus Christ. If the measure of a man can be taken by the quality of the offspring he leaves behind, then Lavoy Finicum was truly a giant amongst men.
You may not agree with his views or actions but there is no way you can think he was anything less than a great human being unless you know nothing of the man or are a very poor judge of character.
