QBs are great for rote learning. The best. You don't need to memorise the questions and answers - there's only so many ways to ask the question if the answer is 1944 or Chicago.
For things like GNAV, they are a tool, but you have to understand how to do the calculations. If I immediately know from looking at the question what the answer is, I'll still go through the motions of working it out. The question banks generally give decent explainations, from which you can learn technique.
For example, let's say you know nothing:
You get a question about PET.
You guess.
Wrong.
It gives you the answer.
You can now (a) memorise the answer,
Or (b) learn how to do the calculation from the explaination, or Google/YouTube it to find out how to do it - and use the other PET questions to confirm that you are doing it right. Guess what? You just learned something from a question bank. And because you had to go looking for it yourself, you will remember it all the more. I couldn't get my head around polar stereographics until I watched a 5 minute YouTube clip, then it made sense. The QB made it stick. There is a lot more to utilising the QBs effectively than just memorising the answers!