I agree the books claims about the brain are mostly nonsense, but it does teach you to draw what you see, instead of what you think you see. I think that is a great first step in learning how to draw, feels very satisfying and gets results quickly
That said, if one doesn't want to take drawing seriously and just want to have fun (See conflicting Amazon reviews on Betty's book), Betty's book perhaps is entertaining. I just have a problem with its popularity and will probably lead people into delusion that somehow they have managed to conquer the drawing. Drawing is hard.
I also lose respect for authors that despite of knowing nothing about the field or making any attempts to study/understand, they have the audacity to publish their own version of "how the brain works". It bothers me.