Polished, to-the-point Product

TLDR: Having tried multiple resources over the course of 12 months, this was the best that I found.

I have used GMAT official guides, Manhattan prep materials, and Math revolution. The first of these doesn't go nearly far enough to get a top score. A common thread in the unofficial materials is that they bulk out their material and call it added value. Manhattan makes you pay for a set of thick books, but when you look at the chapter structure for example they split up the strategy chapters for no other reason than that it allows them to state the same material some 4 times, as a reminder. Math revolution advertises some large number of hours of video content but if you watch the videos each opens and closes with a slow title and again, often repetitive content. This goes further than lacking substance, it detracts from the value of the product as it cuts into your time to discern the value from deliberately included BS.

TTP made the most of my time. All lessons in the quant section were direct and to the point, explaining each topic only so far as I needed to know. After completing all the material you then have a huge question bank to work through. The hard questions are probably harder than what you'll see on the day in many cases, but are excellent examples to test what you've learned. On completion of a practice test you can bookmark problems that you struggled with or guessed, then compile custom tests made up solely of those questions you found tricky. I loved that feature as I got close to test day and wanted to find problems that I knew would inch me closer to the score I wanted.

The newly completed verbal section is not as good. Sometimes it can be long-winded, again unfortunately seeming to pad itself out with examples, or oddly structured, opening with an exception to a rule then going into what the rule was.

Beyond the materials the presentation of the site is great and customer service is highly responsive.

To make the most of the course takes far more than a month in my experience, so be ready for that, but otherwise this is my number 1 recommendation for GMAT prep after you have used the official guide to understand the structure of the test.