If you are talking about the mock exams from the 2 week brush up courses, then I would say that they are representative of the real thing. But if you mean the mock exams generated from the QB, then I would say no.
Obviously the QB questions are very accurate, but I asked BGS the same thing and they said that the QB mock exams are simply a randomly generated selection of questions and therefore don't give a representative spread.
If you have some spare time, I would make sure that you have nailed the mock papers from the brush up course, concentrating on the ones you got wrong or weren't sure about and are comfortable with the exams timings?
Have you gone through the entire QB systematically yet or are you just hitting the generated mock exams? If you have time, do all questions for a subject and then concentrate on the ones you got wrong.
I think if you have nailed the mock papers from the brush up and are keeping your hand in with the QB, you can't go far wrong.
Good luck!