Advanced GMAT Quant is very complex. The problems are definitely challenging and worth reviewing for high-level concepts and multi-step solutions.
The difference is that the real GMAT presents problems that are equal in difficulty but much more "elegant" than
MGMAT, or any other prep company, for that matter.
GMAC finds ways to give you problems at the high levels that seem deceptively easy in their nature, but contain 2-4 levels of easy mistakes that you can make, tripping you up and making you draw incorrect conclusions that lead you to a wrong answer.
I would do
MGMAT Quant to become very proficient at tougher concepts and harder problems, but to score high on the real thing, you need to do a lot of practice at paying close attention to detail on real GMAT problems, and identifying the subtle but devastating mistakes they will often lead you to make. That's ultimately how you'll get a higher quant score. The concepts are the same, but the trickery goes up, significantly.