I actually was in the exact same position as you when I did methods. My school used the Heinemann textbook, but in Year 11 I had used Essentials. I found Essentials a much more comprehensive text with more challenging questions.
What I did was, is I did very basic questions from the Heinemann text, e.g. if we were covering the chain rule I'd just do the simple ones and maybe a few of the extended-response questions. After this, I went through 80% of the exercises per topic in Essentials, this really solidified my knowledge. Not only was I getting more exposure, but I was being challenged.
I think that's the best way to go, it's what I did personally and what worked the best for me. Perhaps do some questions from the Heinemann - or, whatever homework you get set. Then, as I did, read the theory in Essentials and do the questions. Particularly, ensure that you do the extended-response questions at the end of each chapter, those were always really difficult.
Hope that helped!