Does Knewton publishes any GMAT Prep Books?

There was a misunderstanding in one of the discussions here. If you have an official GMAT score, Knewton considers that your baseline score so it really doesn't matter how well you do on their diagnostic test.

5. Guarantee.

(a) GMAT: Knewton guarantees that your future GMAT score will be at least fifty (50) points higher than your baseline score. If it is not, then you shall be entitled to receive a full refund of your Knewton membership fee subject to the following terms:

For students with a valid official GMAT score (defined by GMAC as the score from a GMAT taken less than 5 years ago), that official score serves as your baseline. If you have multiple official scores, the highest score will be used as your baseline. If you do not have a valid official GMAT score, your Knewton diagnostic CAT score will serve as your baseline. For students with multiple accounts and multiple diagnostic scores, the lowest of these scores will serve as your baseline. You must establish your baseline before you access any Knewton classes or resources in the paid course (aside from the first class session) and you must take an official GMAT within your Knewton membership period to qualify for the guarantee. You must complete five (5) Knewton GMAT CATs, attend all class sessions (either live or archived), and complete all required homework for each lesson. Your refund request must be accompanied by an unopened GMAT official score report and must be received by Knewton within sixty (60) days of your test administration. If your baseline is from an official GMAT and that score does not also appear on the recent score report, you must provide an official score report for that administration as well. If you have multiple test administrations after the start of the Knewton course and before the end of your membership period, the highest official score will be used for money-back guarantee purposes. The refund will be made in the original form of payment in US dollars.

So it'll cost 590...
And they refund you if you don't manage to improve your performance by 50 points.
So basically I'd be paying 11.8 dollars per point.
Somehow, I can live with that.