The way I understand it, MicroMesh was originally developed to remove scratches from acrylic aircraft windshields. So yes, it is good for plastics.
When working with acrylics and resins, I much prefer to use wet/dry automotive sandpaper, and I wet sand all the way to 2500 grit. This is approximately the equivalent of 8000 MicroMesh. The plastic needs to be cleaned after each grit to remove all the slurry from that grit, otherwise you will still be sanding with it.
At this point the plastic looks real shiny. A final step can be done with 12000 MM, or with any other plastic polish, or a good finish wax. (ask Pres. Lou about it ...)
I use MicroMesh, but not very often.