I have a ring but not like the one you describe. It's quite light and moves around and isn't stable on a gas hob like mine. No way would I leave a hot wok unattended on such a thing; I feel it would tip over.

The item you speak of would be great but wouldn't it raise the height of the wok somewhat? My gas hob is at work-top height, which is high for using a wok. When I have a lot of food in mine I need to stand on a stool to do some hearty stirring. I'm not particularly short but I reckon I'd feel dwarfed by such an arrangement!

So a flat-bottomed wok is a compromise for me - even though the sides don't get as hot as they should for true stir-frying.