An added thought. Mules are smarter then horses. Therefore mules were used to pull wagons whenever they could be located in numbers. Also, once one gets away from 'hollywood' mules were used to pull stagecoaches in the old west. The horses would be changed out once the stage left a town, then would be replaced with mules until the last stage station before hitting the next large town. Marketing 101, a clean bright stage entering a town pulled by 'clean' horses looked a lot more appealing then dusty old 'annoyed' mules.
So with all the HAT wagons now on the market mules are needed and IMO would in fact sell........even to our metal counter parts.