I was impatiently waiting for this book and prepared to love it. Instead, I was very disappointed. Arguably, Osprey's series often tend to be "hit or miss", largely because authors face severe space constraints - typically no more than 48 pages for Men-at-Arms and 64 for the Elite series - when covering their topic. This booklet faces these problems, but it also has others related to its structure, its contents and to its rather atrocious editing.
First, most of the book, that is the section title "The Regiments - Formation and Organization" (with the term Tagmata meaning "The Regiments") is in fact a summary of John Haldon book, "Byzantine Praetorians", published in 1984, out-of-print for years and rather hard to find. This in itself would not necessarily be a problem and could in fact give value to d'Amato and Rava's book if it wasn't for one fact. Haldon's book covers the period AD 580 (the reforms of Emperor Maurikios) to about AD 900 (roughly the end of the reign of Leo VI who reign 886 - 912). This book, however, covers the period 925-1025 but present the same material in a summarized form. The implicit assumption - which is not even presented in the book - here is that the organization and structure of the Tagmata that existed in 900 did not change for over a hundred years, something that is somewhat difficult to believe.
Second, there is some text on the Regiments formed after 900, in particular the Athanatoi (the Immortals) of John I Tzimiskes and the Varanguard of Basil II, but they get no more than a paragraph, respectively 26 lines and 12 lines for the Varanguard! Even knowing that the authors have published a similar booklet on the Varanguard a couple of years before does not justify such a cursory and superficial treatment.
A third - related - problem is the absence of any description of the battles in which the Tagmata and Guards took part in during what it sometimes called the "Byzantine Reconquista" and which is precisely the period that this book is intended to cover or of any of the members of these regiments (and of their careers and deeds) who fought in them. For me, this was a major disappointment. It also lead to wonder how much genuine research had gone into this book given that the sources for the 10th century do contain materials enough to come up with vignettes on some of the most prominent "guardsmen". Also strange was the bibliography. While it is incomplete, which is again explainable by the book's space constraints, NONE of the translations of the primary sources are mentioned, although most of them are currently available in English. If nothing else, this is hardly helpful for any "amateur" historian or wargamer who would want to learn more about the period. Also absent from the bibliography are some major works on the Byzantine military reconquest, such as Haldon's Warfare, State and Society in the Byzantine World or Whittow's the Making of Byzantium.
Another major problem is the editing, which is so appalling that I even wondered if there had been any. There are so many mistakes that I will not mention them all here. Some are obviously typos that could have easily been avoided, such as the mention of a Domestic of the Scholes being "elected", the mention of an expedition against Moslem Crete in 969 by which time the island was already back in Byzantine hands (it should obviously be 949) or a confusion in the dates of reign of Theophilus (829-842) and of his son (842-867). When discussing the number of the infantry Tagmata (Walls and Noumeroi), there is also a proof-reading/drafting issue: each of the regiments was about 2000 strong and composed of 8 units of 256 men given a total of 16 bandon and about 4000 (4096, if I still know how to count!). There are other examples where the drafting is rather shaky and imprecise.
So, although I understand that the authors' previous book (which I have not yet read) on the Varangian Guard was a success, I cannot vouch for this one: it is simply not good. The only pieces that I really liked were the plates, while the description of equipment and weapons were acceptable but neither original nor outstanding. For me at least, that was simply not enough...