First let me assure people here I am no shill for Wayne's Audio. I've never met him until I bought a ring and a clamp.
I have a Music Hall 9.1. I never play a record without it. It fits the discs well and does not slide around. It seems too heavy to resonate or otherwise move. The guide supplied perfectly centers the periphery clamp. I can see it running true.
I don't know what is meant by "fit the platter". On my Music Hall the disc comes to the edge of the platter. On my Rega it overhangs the platter by about 1/8".
I've been using it for two years and have no complaints.