OG Quant questions are from past GMATs so they cover the same topics in the same way as the GMAT does.

For those at the high end of scoring range (especially for Quant), the OG offers too many easy and intermediate problems and not enough difficult questions.

The OG is fantastic for practice but doesn't do a great job of teaching concepts, so it should be paired with other teaching materials (I'd recommend GMATFix OG Companion and MGMAT Guides)