Soksu means less efficient move. The book is called dictionary but it is not one. The problem diagram index does not justify it. In contrast to Soksu Clinic this book is for single digit kyu players. Dan players might also learn one thing or another but certainly won't read it twice.
The book has a weak structure: Diagrams roughly related to a particular topic are presented in succession. Topics include the struggle to get ahead, aji keshi, direction of play, and using/forming thickness.
There are 40 problems and several commentary diagrams each. These illustrate less efficient shape, more efficient shape, and reasons.
Soksu Dictionary is a typical teaching by examples book. Since it is also written for kyus, I cannot be excited about it. However, it fills a gap of the English go literature, which does not have any noteworthy shape efficiency book.
Is it worth buying? Yes, considering the price. No, considering the necessary effort. My advice: If you happen to see it, buy it. If you can wait a few weeks or months, then buy Charles Matthews' shape book, which may not quite fulfil my dream of a perfect shape book but which will use teaching methods far above just listing examples and will therefore be well worth reading. The other Korean soksu book, Soksu Clinic, is interesting for dan players independently of soon appearing English books.