MGMAT review

our tests have been shown many, many times to have high fidelity to the real test in terms of scores. in other words, your scores on our tests will probably be quite similar to the scores you'll receive on the real exam.

this doesn't mean that you'll get exactly the same score, of course; the exam has a standard error of 30 points, meaning that your score on the real exam could reasonably come anywhere from +50 to -50 points relative to the practice tests.

the one discrepancy between our quant sections and those on the real test is that ours tend to have longer, or more labor-intensive, questions. normally, though, the effect of this discrepancy is to cause higher scores on the official practice tests (and the real exam!), because if you have tight enough time management to get through our longer questions, then you'll be lightning on the actual test.
there are occasionally "innovative" problems that are of new and unfamiliar formats, because the test (and the gmatprep software, whose various updates reflect recent changes in the test) is constantly evolving. we are doing our best to stay on top of those changes.

we of course can't "rate your performance" without much more data about your background, preparation, and performance on the different components of the tests.
if you generate the "assessment reports" that accompany the practice tests, you'll be able to generate a large amount of data that you can use to judge your performance.