I go to Terry Lee for tutoring. He's alright, but watch out for his weird shortcut methods. A lot of teachers won't approve of those methods and deduct marks. Also, if you work on his textbooks, you'll find the questions much harder than what your school would normally give. I mean, we had to do a few exercises from his old Extension 2 book at school, and half the class had no idea what the question was asking and/or how the solution was worked out in the answers section. I haven't seen the 4 unit Cambridge textbook before, but his book might be comparable to that.