I think its a cool idea, but would personally never use one because I don't want my $3000+ bike hanging off my back window..
(Plus I own a pickup truck, so my bike just goes in the bed anyway
With that said, I do think it serves a purpose for those people who don't have room to store a bulky bike rack, or for those who don't need to transport their bikes long distances (i.e. from their house to their local bike shop).
Thanks for posting! It's cool to see some new ideas