That is funny, I think these books are absolutely terrible, along with the main Hardy text. They are just a random mash of conventions that Hardy likes, with cherry-picked example hands to demonstrate their merits. Every example hand or problem in the book is chosen to be painfully obvious, there are no interesting judgment calls of any kind. Also, the tradeoffs involving each convention are not even addressed. Furthermore, many ideas he has are outdated, and newer developments (like two-way NMF or XYZ for example) are not even covered in his yellow book. Most importantly, though they are marketed as 2/1 books, the majority of all of these books has nothing to do with a basic 2/1 framework. In fact, very little detail goes into 2/1 fundamentals, and like I said, it is just a random collection of conventions with mediocre explanations. The books are also just very dry and boring to read. These are the kinds of books that can hold an aspiring bridge player back for years, and I feel bad for anyone who has made the mistake of studying these books with any level of seriousness. There is a reason Hardy never achieved any meaningful level of distinction as a player.