Ed Friedland and Great methodology!
I would say that this is the BEST book and version of the books that you can get for learning bass clef. Ed F is an excellent teacher, writer and bassist. Look him up online. I cannot be 100% sure that he actually wrote every exercise here but they seem to have his style and focus on useful techniques.
This book is meant to be used with a teacher if possible especially if you are a beginner (of any age). But if you are an experienced player that is looking to learn to read music as an independent study this book will be perfect. The fact that all 3 volumes of this method are in one book is really a great value. This can and should be used with other books that concentrate on other aspects of musicianship and Western music theory if you want to advance further, but you will need these basics. If used properly and regularly (with a teacher or without) you can learn to effectively read the bass clef and improve your reading and sight reading. What I find especially good about this book is that there is a focus on the structure of written rhythm. Electric bass playing is so tied in with rhythm that it is important to begin learning it well and challenging oneself from the beginning. Because of the repitition and challenges within the book you will be able to break the music measure up visually and ‘see’ the rhythm before you play it. This alone will raise the level of your sight reading ability to very high level. It is well worth the time to learn, study, and practice from this book.
As an example, if you want to play “walking bass”, after a relatively short time and some instruction about sharps/flats in the music key, you will be able to read most 4/4 walking bass lines from sheet music. That may be within 2 months with diligent practice and some guidance. This book is a “must have”!