My first attempt at the GMAT was after using Kaplan's GMAT 800: Advanced Prep for Advanced Students book. I found it to be helpful with verbal, but the quant section was somewhat lacking.
Taking the GMAT for the second time, I wanted to place more focus on the quant section. A friend referred Target Test Prep after using it for the GRE. I signed up in September but didn't start studying until early/mid October. I would study for about 5-10 hours a week dependent on my schedule.
I loved the interface and detailed explanations for every question. Having the option to review easy, medium and hard questions also helped me gauge how well I understood the lesson. The structure of the material also follows a very logical path and the dashboard clearly shows your progress throughout the course. At first I went through every lesson and quiz, but as the test got closer I started to focus only on the lessons that were indicated as weak areas on my diagnostic test (which is also a great feature to have).
The week of the GMAT I did a few of the larger review tests. An important aspect of my score below is that I did not review verbal at all (outside of 2 full length tests) between the two dates I took the GMAT.
My goal for this second test was to break 700. I needed to feel more confident going into the test and effectively use my time the day of. TTP delivered on both fronts. While my quant score increased less than my verbal did, (Q44-47, V37-42) I wouldn't have gotten a 720 without TTP. I started off with the quant section and felt far more relaxed this time around. Moving into Verbal knowing quant was behind me (and likely better than my first GMAT) was a huge asset and my confidence only grew. I am very happy with my score and would encourage anyone who wants a thorough amount of of practice questions, quizzes and lessons to use TTP.