I took Step I and just tried out the sample questions, and they look pretty good IMHO. I definitely wouldn't use them as a sole mode of study, mainly because you would be missing a lot of important information that is not included in the oh so skimpy First Aid. However, the way the questions are written more strongly resemble actual Step I questions - they are shorter and devoid of typical buzzwords like Q-Bank. I think that I would still use Q-Bank, since doing all of the questions gives you a good range of topics that can be covered on the actual exam, even if the questions are not worded similarly. If anything, USMLERx might be a good source of practice questions on high-yield topics for the exam such as Pharm and Micro right before the exam when you've exhausted Q-Bank and are starting to memorize your notes from First Aid.
Also, if anyone is looking for additional question sources, the NMS questions (~850) are a little more challenging (for some topics) than Q-Bank, but I'm not a fan of the interface.