Currently I am practicing with their verbal section. My impression:
RC is very good. Put it this way - MasterGMAT RC explanations persuaded me that Initial Reading is indeed a useful and efficient way to attack RC questions.
CR is excellent. Explanations are detailed and clear, and many quesitons resemble those dreadful horrors I met on the real test
SC is... good. Explanations and questions are great, but some questions are confusing (i.e. a correct answer may contain 'whether or not' or heavy redundancy. I am going to check my doubts with MGMAT SC
So, if you're hopeless in CR and RC, I highly recommend MasterGMAT course.