I am a fairly skinny girl, and this thing works amazingly perfect for me.
Anytime I tried an SI belt, I could never get it to stay down without sliding up, so I had always just used a back braced squeezed really tight over my hips, but even then, if I moved around too much, it would slide up and I would constantly be pulling it down. But then I found this!! It's a dang game changer!!!