Over the years I've had a few students who've been through these courses, some have been very good but many have not retained sufficient of whatever they were taught. One student told me he'd been on a "guaranteed pass" course (in the south) and failed an exam, the instructor/examiner gave him a small amount of tuition on the questions he'd got wrong and then gave him the same paper and answer sheet back. He passed - surprise!
My approach is to first get people to read the book and then to spend time with me so we can go through the important bits of the syllabus as a Q&A, with me filling-in any gaps or improving their understanding. They then take the exam straight away unless one of us thinks they need more study or tuition. The Q&A time varies with subject and how well prep'd they are, min about 40 minutes and max 2-3 hours. I've had a couple of people do 4 exams in a 12 hour day, but they are the minority and were unusually able and well prep'd. Usually people prepare 2 or 3 subjects.
This seems to produce knowledgeable pilots and a very good first time pass rate.
HFD