I also have exams in 2019 and my teacher also gives us extra case studies and models from the old syllabus, because she thinks they're important. Our one test was a past paper, so they were useful, but honestly we can't know for sure until the first exams if they are useful to the new syllabus. Personally, I focus more on the new textbook, but I will be revising some old stuff too.
As for study tips, I recommend dividing all the advantages, disadavantages, causes, reasons etc. into economic, social and cultural, political and environmental and study it that way, because you can structure essays this way. Some topics from the old syllabus are covered this way on Greenfield geography.