Well, the reason that EatCT is so famous and popular isn’t that it has the best material or the most in depth teaching. The book was written over a hundred years ago, when there was almost no detailed book in existence about sleight of hand with playing cards. It changed the way close up magic was done, and inspired probably the greatest minds in magic, not to mention the danger of writing such book about a topic like that at the late 1800s and early 1900s.
Yes, it is quite hard to understand at some sections, and lacks enough details on some moves, compared to books written after Erdnase, but it is still not really impossible to understand. In fact, for some moves like the stock shuffling or overhand shuffle techniques, even now it is one of the most detailed explanations with probably the most useful techniques on these types of false shuffles. And even though there are improvements on some of the techniques taught on EatCT, every technique written in that book could be used even today if you put enough time and effort on it, and even the routines at the end arent exactly outdated in this era, as the late Ricky Jay used one of the routines in the book with almost the exact style described in Erdnase as a main part of his shows. Not to mention the top card guys who used and still use these moves professionally.
Plus, there is one more rather personal reason that I think this book is worth reading at least once, the writing style, even though at times a bit hard to understand, is a true work of art. The way he describes the moves or the introduction are some of the best English texts that I’ve seen in terms of writing styles. I’ve read even the introduction section at least 10 times and really enjoy just reading the text of the book as a piece of art, and not just as a technical book on sleight of hand with cards.