I use this to keep an electric bass upright against a table. It's almost not big enough for the neck (normal P bass), and it looks like the clamp over the strings might pop open any second (it hasn't yet, though). The material is pretty soft, hard rubber or soft plastic. It cannot support the weight of an electric instrument by itself, the bass still needs to stand on the floor. I wouldn't trust it for one of my more expensive basses.
Having said that, it serves it purpose, and I will continue using it unless a better solution pops up.