the 1st digit is dust protection, 2nd digit is water resistance/proofness. the X means it hasn't been tested.
the e4k is 21700/4-xpl/4400lm/11100cd/211m for bright flood and the mh23 is 18650/1800lm/21600cd/294m, less bright with short-medium throw.
besides both lights being relatively small and of similar form with side switches, imo they are quite different in performance.