I just took my CK on Wednesday and used Kaplan Qbank for a while during and after I completed their live lectures in May. I appreciated it as a good basic introduction to how to approach the types of questions and how to train yourself to think in the CK mindset while I was doing content review. I found that a lot of their questions are constructed around the way they've written some of the text and some of the authors/teachers kind of teach to the test in that regard. I found it helpful to build stamina when having to face longer question stems and learn to sift through the fluff to get to the main point, but it's not your best bet for high quality questions with pristine formatting and great explanations. I studied along with the lecture notes and didn't bother to finish the whole bank. Technicality wise, I found the software to be kind of glitchy and cumbersome, there were a number of typos and after starting UWorld, I didn't look back at Kaplan. As far as the real exam goes, the questions are a lot more like UWorld and the NBMEs/shelves.