I don't interactive [believe] CDs are really necessary.
Just read the book, practice on AirQuiz, re-read the bit of the book that you messed up on and repeat.
Different people learn in different ways. I learn best from books and reading. One of my PPL students found the books impenetrable and went for the Oxford CDs - he is very enthusiastic about them, they did the trick for him.
Before that I considered them a waste of money, but not anymore!