I did not find that at all. Quite the opposite, in fact. The highest I ever scored on a
MGMAT test was 700 - score breakdown was 640, 700, 700, 670, and I ended up with a 740 on the real thing. Their quant is more involved - more steps to each problem, which makes it more difficult to do in the time allotted - and their verbal is, well, just kind of gnarly. The SC parts are clear, but the RC and CR sections I found to be rather more opaque than the real thing. In general, I would say that it is worthwhile to do the
MGMAT tests and really focus on learning from your errors - the tests do give you a real workout in concepts, particularly in quant. In terms of how you will actually score on the real test, there is no substitute for the GMATprep tests, and you should leave yourself time to go through both tests more than once.