"Elon's critics, admirers, and wanna-be entrepreneurs" is a pretty broad category, I think just saying the intended audience is merely people who are interested in Musk.
In terms of tone, I would say candid and colloquial. There is a moment where Vance describes Musk repeatedly asking him [Vance] if he thought he [Musk] was crazy. I feel like Vance leaving this in the book shows that he wants people to understand Musk but also to realize that Musk is just as human as the rest of us are.