As much as Maths in Focus cops a heap of stick on these forums and from discussions from students that I tutor. I feel it is a good book in terms of explaining the basic concepts, examples right. The standard is 'easier' to make sure you get all your foundations right , and I personally like the book because its explained in colour and there are a heap of questions you can do. I have spent around 1 year trying to do all the problems in the Prelim and HSC book and think I have covered around 60% of the questions (putting in 2 hours a night)
In terms of another book which reinforces the concepts I actually recommend a textbook by Lee. Now the book is great because it has again coloured pages, worked out solutions and the questions are of a more challenging level. Also reinforcing material with past exam papers is essential. Look it doesn't hurt to have the whole set of books because I personally think in a busy year like year 11 and 12 it's all about 'time constraints' more than anything.