I've used the platform to study from day 1 of my preparation. It's actually useful for the quant. The problems are diverse and some are really difficult getting you even beyond the scope of the actual GMAT Test.
On the Verbal side, there is room for improvement, the platform offer some good question, but some of them are not as qualitative as GMAT question. Administrators should spend sometime going through verbal question. I'll rather have 5 high-quality CAT than 12 acceptable CAT for the Verbal.
Also the platform should offer the opportunity to run a full GMAT mock exam, including Quant, Verbal, IR and AWA.