I would say the higher price tag is more like "Prusa" using its name as a quality assurance system where if you want to get something working without much hassle (since nearly every other mk4/mk3s clone that has been out there really really sucks except the ones from Prusa) you have to pay the premium.
This is not to say they are necesarrily doing a bad job on open sourcing or abusing, but just a mark that "open source hardware" doesn't necessarily benefit the customer as much as "real world features".