Soksu means less efficient move. The book consists of three parts. The short first part is probably meant to be an introduction into the topic but is a little disappointing and reads more like a selection of 5k-10k problems. The third part is also short, contains problems at maybe a 1k-5k level, and seems to be a test whether the reader has understood the prior contents.
So let's come to the second part, which forms the core. It consists of 36 positions and ca. a dozen explanatory or solution/failure diagrams. One might treat the positions as problems as well but their coverage in the commentary sections goes far beyond what most players would have expected that one should have to read out. Analysis is at dan level and varies between low and high dan. Dan players of all ranks can read the book (and even motivated 5k or stronger). However, a high dan might dismiss it because of rash pride. I tell you: believe Kageyama and do study fundamentals! If you expect to learn something from the book and try to find teaching concepts behind it, then you can learn.
The title might reveal that the topic is about shape efficiency. Although this is right because less efficient shapes are compared to more efficent ones, it is a little misleading. The book is not so one-sided and not just a better/worse comparison. Rather the ca. dozen explanatory diagrams tell you that you have to read tactically if you want to find good lines of plays or confirm their non- existence, which types of lines of plays you should read, which types of move shapes or goal settings are likely leading to interesting lines, and how to make a choice among those. Thus the contents is rather demanding, fruitful, and includes surprising tactics. OTOH, as usual the method of teaching requires you to think about these issues yourself; you are not explicitly taught them because the method of teaching consists of presenting examples and representative lines of plays only. IOW, how much you will learn from the book mainly depends solely on yourself. The examples' difficulty is moderate and so it is rather easy to spend energy on unguided learning but at the same time you should be careful not to consider the level of the book below of what it might be if read sincerely. The book can be read more than once because one can get more from it by increasing one's effort or using a higher level of perception. However, this is like learning moderately difficult joseki several times - it is only moderately exciting.
Summarizing, a dan player who has always missed English shape example books should buy this book or other similar Asian books and read them thoroughly. (The foreign language is not a problem because the text remarks are just short notes.)