I have one that I purchased from George Vance. It is light weight and is fastened behind the neck of the bass with velcro - like a baby's bib. The sock itself provides minimal protection and would not be suitable by clutzy me for transport alone. It is made of two layers of cloth. (Think of a lightweight jacket.) The real protection comes from its location under your fingerboard, bridge arch and tailpiece. And with the bass case covering everything, it provides safe transport.
It is different than the Moridian style cases that slip into the bass cover pocket. As I recall, the one I had had a much tougher, stiffer covering and there was a piece of fiberboard or something along one side.
When I first got the sock, I didn't secure the velcro properly and the bow in sock dropped to the floor.

No damage - but that made me appreciate the phrase "when used properly . . . "
While the sock setup is light, interesting looking, I'm considering a bow case.