Hi Will_I_Ever_Learn,
the book you refer to "The Essential Herbert M. Shelton " is not a book I am familiar with and not addition to my library.
I believe it is a compilation (from looking at the excerpts) of Sheltons ideas and writings gleaned from his other works on Natural Hygiene generally, or what he referred to as Orthopathy/Orthobionomics. If so then this could be a good summary of his teachings and findings within the NH field.
The title suggests it is an autobiography, but Shelton was too modest to write one, or even had the time to do so.
I am therefore unable to comment one way or the other whether this would be the best purchase of his ideas and experience.