I tried it out earlier this year when it was free. I personally didn't like it very much. There were too many totally random questions and what especially bugged me was the quality of the explanations. I felt qbank did a much better job.
This program takes the questions from the PreTest series of review books and are not that much like the USMLE. I used it while it was free and would not reccommend it on top of QBank, or in place of QBank.