When I first purchased Building Walking Bass Lines, I knew how to read notes in the lower five frets of the bass, and played bass at a high beginner's level. I'm also a full-time college teacher (business), so I know solid teaching of any kind when I see it.
Unlike other books on walking bass lines I'd tried to learn from, this book got me walking over chord changes quickly and fluidly, and with a minimum amount of pain.
Friedland gives a brief overview of how to read notes on the electric bass, briefly discusses how to construct chords, and then launches into the clearest and most gradual explanation of how to walk over chord changes I've ever seen. He has a lot of "hands-on", play-along exercises at the end of each concept, and they're stripped of unecessary complexity so you can see the concepts clearly.
A major strength of this book is how you see results in your playing immediately, which encourages you to keep practicing. It's important for anyone learning something for the first time to see immediate progress in their ability, and Friedland has written this book to achieve just that.
The exercises get more and more difficult as you go along, but were never out of reach for me. The end of the book gives the chord changes to 10 jazz standards.
After working through this book, I knew enough to hold my own in a gigging fusion band with some ex-music teachers and university graduates in music.
Also, I found the concepts I learned in the this book made me a better rock and folk player, because I understood how to construct interesting bass lines under chords in any style -- all this was an outgrowth of my jazz knowledge gained from the book.
Anyone who writes that this book is "too easy" or "too basic" is actually complementing Friedland, because it takes a master to dissect a complex topic into something everyone can understand.