I saw them, but never been interested on that product, as usually I'm using only one lens. Can't afford to invest money on accessories which i won't use.
I saw last year a lot of adverts with that product. But myself, I wouldn't trust expensive lens which cost over $1000 to this accessory which I don't know from what material is made. People are using at own risk, but not everyone will be happy to attach an expensive lenses to it. Also don't forget lenses aren't lightweight, so if you attached 2 lenses to it ( depends what lens) then your belt will take you down.