From the mupx docs:
This is the latest development version of Meteor Up and known as mupx. Once mupx becomes stable we’ll merge into master and release as mup.
While mup has been stable for a long time. I know people use mupx too though.
Didn’t know that about stud, so it’s good that I’m using nginx for SSL I suppose.
The latest commit to Cluster was 5 hours ago, so not too sure what you’re talking about there.