Quoted from calvin12:
The issue with a tumbler is it's not suitable for restoration work.
A restoration is an attempt to put back to as close to original as possible. Polishing and shininess isn't part of that process.
That really depends on the part in question. There are plenty of parts that came out of the factory shiny.
I find this conversation a bit of splitting hairs relative to the other things which many of us do; reproduction playfields, plastics and backglasses come to mind. Then throw in a new cabinet and you have a reproduction rather than a restoration. Level of shine on an original part seems silly after all that.