In "Undaunted Courage" it is explained that the repeating capability of the air guns was very impressive to the Native Americans they encountered and usually ensured a peaceful visit. Also, IIRC, they were even used to hunt grizzly along the way (sounds like they were much more numerous and widespread back then). It does not mention it being problematic in maintenance, so that is impressive as well considering the varied conditions and modes of transport and exposure to elements. Sort of like showing up to a knife fight with a M240.
I'm sure a replica of these would sell. Very unique and an important gun in opening up the West.