I studied for three months, about 15 hours a week, using
Magoosh and got a 600 on my GMAT Prep CAT. I felt ok, but took the GMAT and got a 530 (32V, 29Q). I switched tactics and signed up for GMATClub, Veritas Q bank, and read some reviews and found EmpowerGMAT had great feedback at a reasonable price. I struggled with quant but the strategies from Empower were much easier. I won't give away their secrets, but I was able to improve fairly dramatically. Oddly enough, my
MGMAT CATs weren't great - I went from 560 to 550 to 540, but my last test was interrupted by a concert underneath the library! I practiced everything Rich and Max taught me and came out of the testing center with a 650 - 41V/38Q!! All I can say is that I should have gone to Empower first and save myself time, but even with that I spent $500 total in prep costs.