TTP provides a systematic, no-frills approach to learning the necessary math skills needed to do well on the Quant portion of the GRE. To give you an idea of how effective their system is, I usually perform better on the verbal sections of standardized exams vs. quant. On the GRE, I performed better on the Quant. And I only needed to take the exam once. I followed their advice - don't take the exam until you are ready.
What I love is how they own their approach: there are no shortcuts. To do well on the GRE Quant, you must be systematic and be persistent. In other words, learn all of the needed skills, then practice like crazy. TTP will guide you through all of that.