I decided to return to graduate school for a career change after a successful career in the arts began to grow stale. I decided to pursue engineering, however, I hadn't done any academic mathematics whatsoever for approximately fifteen years, and my undergraduate math ended with pre-Calc. I knew I would need a lot of help.
In month 1, I pursued self-guided study, using resources from gregmat, Magoosh, ETS as well as the entire Manhattan Prep math review. The gains were modest -- a five point improvement. I decided I needed the most comprehensive and rigorous course available, and after some research, I settled on TTP.
The site estimates that it will require around 180 hours to complete the course if you are aiming for a Quant score above 165. In my case, this turned out to be an underestimate -- my rough calculations suggest that I spent between 250 and 275 hours on prep, practice exams and taking the test itself multiple times. About 2/3rds of that was spent in TTP.
PROS: My absolute favorite thing about TTP is that it is honest. I wasn't happy when I realized how long it was going to take for me to get up to speed, but I was much better off knowing than not knowing. They do a very good job of emphasizing the way people tend to slack off in their GRE prep, and how that can impact score.
I found the TTP lessons to be the most engaging, comprehensive and well-ordered, by far. They don't cover 100 percent of what you'll need, but 90-95 percent, yes. Their lessons on arithmetic, number theory, ratios, fractions, exponents, word problems and functions were, for my purposes, flawless, and even the weakest sections on the site were still very good.
The website is well-designed and can be used on many different platforms, including tablet PCs, without any issues. Their quizzes do a better job of emulating the real GRE than any other prep service I used. They even nailed the weird GRE calculator, which accepts multiplication and division via the keyboard, but not addition and subtraction! The analytics were useful in targeting my weak points.
CONS: I found that TTP was not sufficiently comprehensive in several key areas on the GRE, specifically geometry, coordinate plane geometry, combinatorics and probability and weighted averages. I needed to supplement in these areas with other services.
Although TTP has a huge problem set, it still isn't large enough to be a one stop shop. I drilled on at least a thousand non-TTP problems from various other services, and that was completely necessary.
SUMMARY: I would highly recommend TTP as the centerpiece service for anyone seeking a truly comprehensive GRE quant course. All by itself, it will get you 90% of the way there, far more than any other service I tried, and if you follow its order and structure VERY CLOSELY, it works. If you skip around and don't do all your reviews and practice exams, it will not work. Trust me, I learned the hard way.