Ācariya Anuruddha's Saṅgaha is in essence an ancient relational database which attempts to comprehend all of the objects of insight collected and systematized within the enormous basket of texts known as the Abhidhamma. It consists of little more than lists arranged in relation to other lists, always declaring the total number of objects in the resulting matrix, like the result of a relational database query. While purely textual, the source material yields immediately to tabulation, and the editors have included many useful tables. They have also included guided explanations of most every topic referenced in the Saṅgaha. This copious editorial material is the saving grace for the modern reader, rescuing a text that would otherwise remain profoundly obscure. It has the side effect of providing concise explanatory material for a great many technical concepts that one encounters in other texts. While it is a prodigious feat, I'm sure the editors would be the first to admit that it is grossly insufficient to confer clear understanding to the average reader of these broad and deep topics on its own.
The great advantage of the Saṅgaha's (and its source texts') approach lies in the delicate subtlety of the phenomena which are its objects. Descartes' application of mathematical ideas to the Cartesian plane was transformative because subtle ideas can only be grasped through the patterns formed by their mutual relations. Even in the suttas there is a great emphasis on lists of terms, which are transposed and compared over and over in various permutations. It is easy for a modern reader to imagine this is merely some literary fashion or artifact of oral transmission. But in fact it is a masterful way of energetically preserving the core meanings of the teaching and insulating them from the vagaries of time and translation. When we learn a second language, we acquire vocabulary which we imagine we can map cleanly on to that of our native language. Even if we know this is not the case in reality, it is the default and automatic position of our cognitive process, steeped in our native linguistic framework and habits. It is only through an enormous amount of exposure to words in combination and context that we discover how the true meanings are far more nuanced, divergent, and represent matrices of signification that may not be reduced to simple 1:1 relations. The Buddha's lists and their permutations carefully conserve a meaning, clear but not obvious, which transcends any language. The systematic approach of the Abhidhamma uncovers the grammar of this endeavor so that we can become sensitive to its purpose and results.
But like any presentation of grammar, the system itself cannot substitute for the vitality of the language in process. The attempt to conform the phenomenon to an analytical structure yields oddities and exceptions (even when disavowed or dissolved by dissection). The real measure of the practice is a recognition grasped by the wise, not conformation to the pedantry of the grammarian. For this reason, such a manual can be of great utility to the practitioner with an analytical bent, but care must be taken not to reify the system itself and allow it to become an obsctruction.
Aside:
While the sequence of the text is consistent with its analytic frame of development, I found it counter intuitive. The physicist might choose to develop a description of the universe beginning with quarks and atoms due to aesthetic or analytical concerns, but the practical history of experiment and inquiry begins with gross objects of experience: the falling apple, the burning fire, the visible stars. The Saṅgaha begins with cittas and cetasikas: the quarks and atoms of the mental universe. I think this is the rare book that may actually benefit from being read literally "backwards and forwards." The practitioner will find much more familiar material in the later Compendia on Categories and Meditation Subjects, but the Compendium on Conditionality sandwiched between them was totally impenetrable for me. In any case, I think there is no escaping frequent cross-reference if the novice is to attain any benefit.