It's practice – USMLE Step 1 Practice Q&A Review

It works for practicing the questions but there are some glitches like others have mentioned. There isn't any way to only answer the only questions that you haven't seen yet. So, you'll finish a set it will say you haven't completed 3 or 4 but then when you try to go back, there is no way of just going through those. (Either that or it doesn't count them/have them to answer.) Also, I have come across questions where the response set or the explanation has been swapped between questions. I was able to download to other devices, but it looks like it will make you pay for it. I held my breath and hit ok and then it popped up with a message that said I had already purchased it and downloaded it without charging. That said, it doesn't communicate between the two which question you have already completed so I have ended up just using my phone.
Review by Mrws on USMLE Step 1 Practice Q&A.