Target Test Prep: 5 Stars

Strengths:

-Comprehensive Quant and Verbal material
-Flexible Self-Study course - perfect for busy schedule
-Great customer support
-Guidance on best practices to prepare for test

Would make the product better:

Sentence correction got into details not often tested. Would have appreciated a warning that it's fine not to get 100% of the Hard questions

Fantastic course for self-study. I used to improve my score from a 590 to 740 in 4 months time. It took me about 3 months to get through all the fundamental material and from there I started using a combination of TTP questions and official GMAT practice tests to get ready for the actual exam.
Their flexible program was great for someone who works in consulting and can have a varying schedule. They also have a calendar that helps you pace yourself (although I found that for me, alternating between verbal and quant throughout my study process allowed me to feel motivated and not get too overloaded with one topic). Also, they have great guidance on the best ways to study, such as not feeling the need to use the dry erase board right away until a month before taking the test.

I recommend it to all my friends starting the GMAT study process or ones that need to strengthen up in certain areas (especially in quant). Some other things to note are that the customer service is fantastic and they'll get back to you very quickly about any questions you may have.