Quote: 'am i right to think that he goes through the exam that you will take and basically just gives you the correct answers?'
If this was the case there would be little point in setting the exam. You do need to understand the subject if you want to be a safe pilot. Give Derek some credit, he is good at getting the subject over. His USP is he sits you in his kitchen and fills your head with the subject for a day after which you take the exam. It appears to be very effective , he has a good pass rate and I've never heard a bad word said of him. If as you say you are short of time and lack the ability to read books effectively go and see him.