It ain't a flotation device, I'd ather bounce on back and let some of the energy be absorbed before being thrown on my face than landing full force on my back.
If you're sliding on your back down the highway nice to know you head will be elevated of the pavement.
Unless yoou can come up with a suit that inflates like the Michelin man there will always be exposed areas but more protection is better than some and some is better than nothing.