Qbank sucks.
Let me give some examples from a few recent tests I took in microbio and immuno.
First of all, their questions are poorly written. They want you to recall obscure facts such as Paul Bunnell antigens, and layer of the epidermis HPV infects. None of this crap is in Big Robbins, Goljian, and not even wikipedia.
Second, some of their questions have wrong answers. For example, one question said IgE mediated worm killing is Type 1 hypersensitivity, which we all know is wrong. Another said, densensitization therapy is used to induce Th1 response, which again is wrong. I checked several sources that said allergic desensitization is used to induce anti-IgE IgG.
Third, their photomicrographs for the questions are messed up. In an identification question, they had an arrow (supposedly) pointing to a nucleous, but the arrow was bigger than the cell itself and it looked like it was pointing to the cell. In addition, a lot of the pictures lack resolution and they want you figure out looking at some blur.
Fourth, their explanations suck big time. A lot of the questions simply have high yield facts associated with the questions, which in no way help you reason why the answer is correct or incorrect.
The funny thing is that I am scoring way higher on USMLE World than I was on qbank. The former relies on logical processes to arrive at an answer, while the latter simply wants you to recall facts and put 2 and 2 together. Given my experience with shelf exams, the NBME wants you to be logical and not some memory machine.