Mpingo discs are ridiculous and utterly useless, except as coasters maybe if they're large enough. I can leave 4 acoustic guitars out (along with a piano that's always there) in my listening room and my rig remains unaffected, although if loud enough the guitars might vibrate a little. Years ago I was visiting a neighbor who was a serious gear reviewer and the Mook freaks had been to his place (a large dedicated and serious listening room…amazing) and "tuned" it with various discs…on stands…stuck to the wall…none of them did anything at all. They became a joke among the "non myth based" audio community along with Tice clocks and other mystical faith based audio silliness. Geoffkait seemingly never met an imaginary tweak he didn't think was real, and markets his own stuff like a bag of magic pebbles…so you can see where he's coming from.