The Bristol question bank - based on my experiences over the past 18 months - contains the vast majority of the questions that the CAA could ever dream of asking you. The questions you see in the question bank will nearly always appear word-for-word in the actual exam paper. With this in mind, a lot of students that I came across would simply memorise every question, which can, with lots of hours of 'study', get you through the exams with respectable grades, but as soon as the CAA throws a new question into a paper, these students are stumped! When I sat the exam for Radio Navigation in mid to late 2009, a number of students failed because so few of the questions they had memorised actually appeared in the paper.
If you use the Bristol question bank along with lots of self-study using course manuals, you can't go wrong. But if you plan to just memorise everything you see, then you will most likely get caught out in one or all of your exams. And with every exam that you fail, it's another £86 down the drain.