The only reason to read this book is if you are a big fan of the show and even then I wouldn't necessarily recommend it. It's like reading an episode of a TV show that is only meant to be playing in the background. There is nothing to miss or any real story to follow, the characters are quite simple and written in a distinct style so that they are easily recognizable. For SPN fans it's nice to see a bit of the everyday Winchesters, but "a mundane case for the Winchesters not worthy of a TV show episode" is a strange pitch for a book.