I am not a postal stationary collector, so I can't appreciate the depth of the study this book covers. On the other hand, I believe it is a beautiful publication, in that is has excellent pictures and in color. There is a lot of write up and detailed photos to accompany the full images of what is included in the books. If you can read Spanish, it seems to be a good book. The short comings are the valuations and the comprehensive aspects of the work.
Valuations are limited to only five categories, A-E, and these tell us very little, considering there is no separation between the mint and used. As far as I can tell this would be akin to saying common, difficult, scarce, rare or extremely rare. He list it as Corriente, Poco frecuente, Raro, Muy raro and Excepcional. Personally, I don't think the idea of rare can be broken down into three catagories, so I figure my ratings are more in line with the way an English speaking person would say them. Anyway, the question is, what is it? Mint or Used? I think that this area of the study needs the break down between the mint and used examples, or he would have been better to skip evaluations and forget the idea of a catalogue premise.
The second point that the book is not really comprehensive, for completeness, not showing all known items available to the collector. This is a problem, if this work is also to be considered as a catalogue. So, I can understand Jerry's point in this area as well. Care should have been taken to at least list items that are available even if the author could not produce picture copy of such items.
As for the books, I believe every collector of the postal stationary of Mexico should have one of these for the numerous details that are included on what is in the book. Personally as a seller of Postal Stationary, I feel it will be helpful in finding out things about some of these issues that are missing in other works, or let me say make them more understandable.
Bottom line is the work is of Sr. Zavala's personal collection, it is beautifully done and it does breath in the romance of collecting these items. I say, it is worth buying, if you understand it only goes so far as a catalogue. Treat it as an extended article on Mexican Postal Stationary.