Had a couple of lessons in one... It made things clearer but dont think it has permanently changed my riding as i'm still not sure on the MWT....! Im no help really!
I'm picking mine up this week. I think it will focus you on using your stomach muscles correctly etc, I even had tried this using a towel tied round my waist until i had the belt. I dont think it can do any harm..
I always wear a back brace as i have a conjoined spine, and my Mary Wanless instructor told me it had exactly the same affect, just holds you in a bit and makes you aware of wear your core muscles are, gives you something to "beardown" into
It goes around your waist and you sort of hook your fingers in it. I think its supposed to make you more aware of your core, something about not hollowing your spine. Might be a bit gimmicky. Anythings worth a try!
I have one and to be honest I don't feel any benefit. Hooking my thumbs into the loop means I can't move my arms. But then I've only used it twice so I'll keep trying