Here are just a few of the people who support GBT, please check them out.

"Garage Band Theory is a must for any musician."

Rolling Stone Article:

Emmylou Harris and Rodney Crowell Come Full Circle on ‘Old Yellow Moon’

"Don't be put off by this giant book - Duke's got the secrets of the universe in here. Quite simply, this is the most comprehensive book on music theory I've ever seen."
"Something for every musician at any level. Especially helpful is the musical notation and tablature for a variety of instruments. This book inspires me to learn and practice more."
"Garage Band Theory is a veritable encyclopedia of useful tools and tips. This book lifts the lid off the “black box” of music theory and let’s the light shine in – and in a fun, practical way. This is a book which should be left handily lying around the living room, bedside, studio, classroom, (restroom?) – ready to be dipped into at any time for reference purposes or just to improve or refresh one’s fluency in the language of music. A great resource for musicians young and old no matter what your training. For the price of a one-hour lesson, GBT offers a lifetime of learning."
"Garage Band Theory let me know how little I know... but in a good way. Great Book!"
"Garage Band Theory offers you everything you need to know to understand, play and make your own music. Because he is both an accomplished musician and teacher, Duke Sharp is an excellent guide for beginners and more advanced players alike."
"This book is written in the people’s key."