This is the kind of book that you probably won't fully understand the first time you read it. Not only because it was published in 1902, and therefore containing occasionally archaic language, but because there is so much finesse and subtlety packed into the descriptions of each technique. Sometimes, when studying one move from the book, the description will provide an extra clue as to the execution of another sleight. This is a book that should be your constant companion, to be read and reread over and over again.
Erdnase starts you off apparently fairly slowly and easily, with some overhand shuffle technique, but even there, he includes gems of insight and elegance that it is very easy to gloss over on first reading. He takes you all the way to shifts that will seem impossible when you first try to tackle them. My recommendation, therefore, is to not study Erdnase exclusively, expecting to master it all before you move onto something else. Familiarise yourself with the text, and the mechanics of the moves, and then return to them every now and then to polish and smooth the rough corners, gradually adding the finesse that he describes, and making new discoveries on the way.
So, to answer your question more directly. Yes, it's pretty hard, but properly studied it will improve all your magic.