I didn't have access to the QB due to internet access problems, but I gather it is pretty good. I'll will bore you with two contrasting tales.
At Bristol's brush up course you will find that you do a week of lectures on the main area of Gen Nav that come up in the exams, and a second week where you do 'past exam papers' during the day, followed by more as homework. This is great preparation...assuming that the area that Bristol concentrate on are similar to the areas the CAA concentrate on. As it turned out in the Feb Gen Nav exam, the two do not always coincide, leaving many people who did well on the course worried about failure.
The second tale relates to Human and the two Comms exams. Here the QB - or should I say the 'past questions' - provided by Bristol prepares you very well for the actual exam. Maybe we were lucky, but I went through the available feedback questions only once before the exams, going over the ones I got wrong, to see why, and then got 96% for Human and 100% for each of the Comms exams. Now, I am no genius. Without the QB/feedback questions from Bristol, I would not have done as well.
I shall definitely get the QB for Module 2. My plan is to go through the notes fairly quickly and then do the QB religiously until the Brush up course.