Mixing sensitive reactions that preserve mixing results in the product distribution can be used to characterize mixing devices. The competitive-consecutive reaction of bromine with 1,3,5-trimethoxybenzene was applied to four static mixer devices ranging in size from several millimeters to several micrometers. The commonly used parallel-competitive reaction of iodate and borate with acid was also used for comparison purposes. Both methods were suitable for characterizing all mixing devices. The iodide/iodate reaction method required the use of multiple concentrations of the reactants in the feed streams, whereas the bromination reaction method allowed characterization of all devices at the same feed concentrations. Only devices characterized at the same reactant concentrations can be directly compared.