I have taken Manhattan Prep CATs multiple times, and each time it has exceeded my expectations. Though there are always some questions which seem to be out of GMAT's league but overall the tests have been extremely helpful in determining which section should be attempted first and the pattern. Secondly, it gives a unique experience of how GMAT will appear on the actual date.
I recommend the future GMAT test takers to use MPrep's CATs to correctly identify where they are going wrong and what else cant hey do improve on their performance.
Also, the solutions are very good! One must look at the solutions of the questions that you have done wrong.