You must have GIMP Python working
-- the plug-in needs to be able to display a file selection dialog so you can choose a filename if your image doesn't already have one, and script-fu can't do that.It will show up in your File menu as Save-export clean, probably right under Save a copy.
I saved the script as directed and made it executable via Thunar but I don't see "Save-export clean".
What is "You must have GIMP Python working"??