Dr Du is really good at teaching maths, however, you need to complete a test and be placed in the A class which has all the good teachers. Also being in the A class means you would be doing material like 1 year ahead of normal school curriculums.
Dr Du is very good for maths. It works very fast and far ahead, and its HW questions are difficult and excellent. You get a weekly quiz which helps you to identify weaknesses and improve exam technique, and the spirit of competition is very high. The classes are graded, and the only difference is some harder questions. All the content is relevant to the HSC.
For teaching, Dr Du has alot of focus of proving the things you use and deriving formulas, etc. which can make it 'conceptually difficult'. Personally I think this is a good thing, it actually helps for better understanding. If you get a bad tutor, they might just read off the lecture notes, but there are some good tutors who go beyond that to teach.
For price, its comparatively cheap to say Matrix or Talent, at least before yr12. Check website.