I got this from them:
Even though there is no correlation with real exam scores, you should be in very good shape if you score over cum-performance 55-60%% in our Qbank, this is based on the feedback that we received from previous exam takers.
Also they said this:
Use our QBank as a learning tool instead of assessment tool.
Try to go over all questions number of times and read the explanations for 2-3 times.