The best thing about this book is the way the content is delivered to the reader. The style is informal, but very effective at getting the points across. For beginners it's probably very easy to understand, and for those of us with shelves full of other guitar books it appears to look at topics from a slightly different point of view.
You find yourself reading on a topic you sort of understand only to find it wasn't half as complicated as you first thought. This fresh perspective brought a lot of stuff together for me, and filled in a few holes.
I've only just started the workout, so I can't comment on that yet. But it looks promising.
My only criticism - the author stops a bit short on some topics and leaves you wanting more information - but maybe that's for another book, so long as it's by the same author.