I'm not a classical player, but I need 'm. Simply for the higher position, & to lean on it with my left arm. It's a guide while finding the positions, too.
But what I need even more is the body contour. Developing my EUB, We found out that, especially when using a bow, it's necessary to have three places to fix the bass against your body (I found out, using my AUB): neck, upper part of the body contour (the back of the bass in fact) and the lower body contour against my lower leg. So I made a body contour. See
http://www.voxhumana.nl for it. Good Luck!