Can't speak for the Spinners; they wre always treated as a joke when I was involved with the folk world, but I bought something similar for ukulele a while back from Eagle Music - toughened, non stretch, fabric with bent metal piece inside which hooks on the lower part of the sound hole.

Whether they do one big enough for guitar or even whether still sell them I don't know; the search facility on their website is little short of pathetic.

I did see an interesting device at a guitar show a couple of years ago. It consisted of a harness which went round your shoullders with a clip at the front and a spiggot which attached to the back of your instrument with suckers. Looked reasonably stable; the person demonstrating the thing was spinning a guitar round on it. No don't remember the name and suspect the product has since gone to the wall the usual way of such novelties.