This is a very scientific approach to shadows. It is all about the geometry.
The order of the book is a little confusing, as you get taught some principles in the wrong order (having taken time to go through a lot of the activities) but nevertheless it is brilliant.
The content at the back is a little weaker but only as it lacks much meat compared to the start.
To add more value, the videos that go alongside the content are probably too much to consume. I doubt I'll ever use all of them. But it's great to have them there when/if they are needed.