Hello folks,
Gave GMAT recently and got 770 (49Q, 49V). I must say that the MGMAT SC book single handedly helped me gain 3-4 points on verbal by improving my SC accuracy.
I also gave 4 MGMAT online exams and I am listing them to give an idea how they correlate to the real exam;
MGMAT CAT 1 690 Q 45 (tough!) V 39 (ok)
MGMAT CAT 2 720 Q 49 (ok) V 39 (ok)
MGMAT CAT 3 730 Q 49 (timing issue) V 40 (ok)
MGMAT CAT 4 750 Q 48 (timing issue) V 45 (good)
I feel like the MGMAT scoring algortihm is very good. I almost feel like CAT 4 is closest to what your score would be in the real exam.
My advice to MGMAT folks would be to make the verbal a little simpler and more representative in the CAT's. As you can see, I never scored great on MGMAT verbal, but always scored in the 99% in GMAT prep and scored a 49 (way above 99% threshold) in the real exam.