A number of approaches have been employed to assess the performance of various mixers in the literature including the Bourne and Villermeux-Dushman protocols, which use mixing dependent reactions at different flow rates to evaluate mixing time. While such protocols are useful in benchmarking mixing performance in a general way, we opted for a more specific approach using the lithiation of an electron-rich aryl bromide followed by reaction with an electrophile (Scheme 2); an approach favoured by those working on lithium-halogen exchange in flow. Scheme 2: The test reaction used to characterise the mixers studied.