Must have if your target is above Q85

Strengths:

The Quant section - it tests the advanced concepts that are well within the scope of GMAT

Would make the product better:

It is perfect, don't have any specific recommendation from my end.

It is one of the best adaptive tests amongst all the others in the market. When you reach to a level where tough questions are asked, the questions won't test any out of scope concept, it would rather measure your higher order thinking, which the GMAT tests.

In case you're targeting a Quant score above the 90th percentile, I would strongly recommend to utilise this product.

With respect to the Verbal section, I won't say that it exactly resembles the quality of questions asked on the GMAT, but that's the case with all third party test providers and only official GMATPrep tests do justice to the Verbal section.