Yes, the 6 GMAT Official Practice Exams (each of which can be reset at least twice), formerly known as the GMATPrep exams, are the most realistic practice exams on the market. However, the scoring is less reliable, and most will find the real GMAT to be a bit harder, especially on the high end of scores. To be safe, subtract 20-30 points from your GMATPrep score to estimate your likely score on the real GMAT.
I considered making a video for this post, but then I realized it was unnecessary. If we simply compare the thousands of ESRs (Enhanced Score Reports) we have seen from the real GMAT to the many studies done on the GMATPrep software and GMAT Official Practice Exams, it becomes quite clear that the scoring algorithm behaves much differently on the real exam.