Sources and uses of funds are a much more reliable indicator of who someone is, who their friends are, and what they believe than the stories they publicly vocalize to themselves and others.
From the perspective of the American experiment in democratic rule of law, my feeling is that Snowden's work has had both positive and negative impacts. Maybe net positive because of increased scrutiny over the natsec apparatus and elevation of "privacy" from a govt perspective (though IMV corporate invasions of privacy are far more profound and impactful and have only deepened); net negative because of the increase in chaos and distrust in governing (I see a direct line from Snowden to Trump).
It's one thing if these are the ebbs and flows of an open society.
Many people in the natsec apparatus- yes, at the institutional level attacked by Snowden- have counterclaims that Snowden's narrative of his actions and motivations is incomplete, that there is more to the story, that there are other reasons he lives now in Russia, which is not an entity that is conducting an experiment in democracy.
To put Snowden's work in better perspective, I would like to see- his use and sources of cash. That's all. And that's not this book.