It is not necessary to use a Study Text if you are watching my free lectures.
However, what is essential is that you buy a Revision Kit from one of the ACCA Approved Publishers. It is full of exam-standard questions to practice after you have finished studying. Practice is vital to passing the exam.
If you use our notes and lectures, and work through every question in your Revision Kit, then you will certainly have more than enough knowledge to be able to get 80+ marks.