I can field this one as a tutor who takes the official practice tests about once a year. There is no need to create a new account through mba.com, since you can simply hit the Reset button in the Practice Exams section and take those same tests as many times as you like. Also, because both are real Computer-Adaptive Tests (CATs), you can take them multiple times and still see different questions, depending on how you tend to answer what is up on the screen. It may not be optimal in terms of a study strategy--you will see some repeat questions--but practicing official questions is invaluable. Just do not assume that if you ace a retake, perhaps with a score increase of 100 points, your actual exam will follow suit. Keep practicing, get your hands on as many different official questions as you can, and take the time to break down where you tend to make the same sorts of mistakes. Then, you will stand to make substantial gains.
Good luck as you continue your studies.