Now, Victor Sanchez is hardly a "disinterested observer" (being that he has his own series of courses and workshops), but, having at least been in personal contact with Castaneda (it is unclear whether Sanchez "studied" with him or not, or simply had interviews/conversations on assorted topics), he's in a good position to package the materials up like this.
Whether the "donjuanist" material really lends itself to this approach is another question. This is hardly like Serge King's Urban Shaman which has exercises and workings that nearly anybody could do in the context of their daily lives. Much of what Sanchez details here requires significant access to isolated natural settings, and many things are structured to take several months of dedicated work. That is not to say that there aren't immediately useful exercises and instructions in the book, for there are (such as types of breathing, dream work, etc.), but the "take away" I had was that most of this work was for folks who could afford to take off a year and run away to the desert!
Frankly, I was disappointed that there wasn't very clear instructions for "working with the Assemblage Point", which seems to be such a key element in the Castaneda books. Over the years I have done quite a lot of Shamanic "energy work" and, while having a pretty good fix on most of the other "energetic" descriptions in the material, am still unclear, from a activity standpoint, what exactly don Juan means by the "Assemblage Point" and what is involved in shifting it. I had hoped that this book would address this central concept, but it seems to skim past it into materials that are, perhaps, more central to Sanchez's work.
Despite these caveats, this is a very useful book. Aside from the main part (which is "concept descriptions" coupled with exercises), there is a glossary of techniques which references particular page numbers in the various Castaneda book, making it fairly easy for one to go back to the source material even when this is spread out over several volumes.
The Teachings of Don Carlos is still in print, so should be available from your local stores, but can also be had for under two bucks new from the Amazon new/used vendors. If you've read several of the Castaneda books, you might well consider adding this to the mix ... I just wish there were more book following this approach out there for other metaphysical traditions!