As far as the Study Text is concerned, then it is OK to use it (although if you are watching my free lectures then you do not really need a Study Text because the lectures are a complete free course).
More important is a Revision Kit (because they contain lots of exam standard questions for practice, and practice is vital to passing the exam). For this it is best to have a current edition because the format of the exam has changed, and the current edition has questions in the new exam format/style.