Speaking as someone who has loved pre war rural blues for 45 years, someone who once had a complete collection of Yazoo records on vinyl including the long-deleted Yazoo 1001... I found this book utterly banal and simplistic. The biggest thrill to be had from it was reading the quotes from songs of my heroes but when I started looking up key blues phrases such as "Mojo" I found Calt's vision sterile to say the least. This happens a lot with books coming from the USA, this sterility of content, total lack of flair and the ability to conjure up something that looks like scholarship but is neither that not a poetic response to the material.
If you are interested in the blues in a human way there are many better books than this, much better, Deep Blues by Robert Palmer for a start.The Lomax and Davis books are also both great. Don't bother with this one unless you are so naive you can't understand basic slang.