The former reviewer doesn't seem to know anything about the I Ching, Chinese Astrology, or how books were written in old China. There _does_ exist a He Luo Li Shu manuscript of which Sherril & Chu's book is a translation, in fact, I have several Chinese versions of it on my shelves. This manuscript uses the so-called Four Pillars of Chinese Astrology and links them with the eight trigrams in a way which is perfectly acceptable according to Chinese numerology. The reason why the introduction in S&C's translation is so terse, is that the Chinese original doesn't give any explanation about the workings of the system either. And that is very Chinese: don't ask _how_ the system works, just see if it works for _you_.
The calculations in S&C's book help you to calculate your Four Pillars. These calculations are not found in the Chinese original, because in China everybody already knows their Four Pillars. And S&C's calculations are just one way of many to get your FP's. Complex? Yes, but it would be useless to explain why they choose this method, because it would not add anything to the subject of the book.
The Chinese original explains each hexagram in terms of 'you will (not) get rich, you will (not) have many childeren, you will (not) have a high place in society', etc.; this is what most Chinese people were/are interested in. S&C give a more Western approach, adding psychological elements about character and capabilities.
The former reviewer has experienced that the system works. In China that would be sufficient. And S&C's translation is a very Chinese book.