they are the same thing in almost all aspects but weld Quality. And KM is getting much better about that judging from personal accounts. And they pretty much cost the exact same amount, so it's solely based on aesthetics whether you know it or not.
They pull the same, they look similar, MZ has a slightly better weld quality as of now, KM's tend to have more parts that are brass, KM's at times tend to rust easier (this i'm saying from experience) because some stems aren't made as high quality as other stems in the KM line.
I'm sure the last one is relative and maybe water ended up sitting in my KM overnight that i missed somehow.