OneChronos cofounder here. The NMS order protection rule certainly doesn't make things easier, but periodic auctions have a unique compliance and fairness advan

OneChronos cofounder here. The NMS order protection rule certainly doesn't make things easier, but periodic auctions have a unique compliance and fairness advantage there. The question most continuous limit order books face is "What is NBBO right now?" That question can't be answered thanks to the speed of light being finite. But because of the way our auctions allow time for orders and market data to arrive at the matching engine, we can more thoughtfully construct a consistent view of "What was NBBO 1 millisecond ago, at the moment we struck our auction?" This is a much easier question to answer, and also has the effect of smoothing out network jitter, data gaps, etc. Also, the auctions are combinatorial but are computed across linear components (stock symbols). NBBO applies to symbols individually, so it can be taken into account as a standard constraint on each symbol.