If you want to read about Nina Simone, I suggest you read her autobiography "I put a spell on you", instead of Acker's biography. Acker's book quotes the autobiography so often, you might as well read the whole entire book!
This is detailed and accurate enough. It reads like you'd expect a textbook to read, which is fine for what it is. It just doesn't provide any insight or elaboration. Which again is fine for a textbook, and it seems this is meant to be that kind of publication.