I'm currently using it (All 3 sciences) and I think it's brilliant; it's a great motivator as it has all the questions ready for you to complete whenever you like. I'm currently at 15%, which doesn't sound like a lot but I'm more than on track to finish it by GCSEs. Whilst it is rather costly, the price can be justified through the website's effectiveness. One thing that I would suggest whilst doing it, is that, and it may seem obvious: make sure you really read all the information and understand the answer - I sometimes find myself trying to make sure I get the answer right than actually getting it right and remembering the answer paired with the question. Given the importance of GCSEs, I'd suggest getting it.