Search it on YouTube what you don't get. I own Edexcel AS Maths because I had coupon code which gave me the course in £17. I think there are much better teachers out there on YouTube who explain the concept better than the one in snaprevise (well after all he's still a student) and I would personally like to study from a teacher. Also he makes quite a few mistakes than apologises and corrects which is understandable but I wouldn't prefer learn in this way. I own OCR AS Biology and Chemistry too. I recommend for Biology and Chemistry.