I used some briefly fourteen years ago; they worked but obviously limit the speed. You'll want them off as soon as possible.
Apropos of which - it's now illegal to drive in the Alps without snow chains (I assume just in winter, but I don't know) and as a result there are *loads* of places selling or renting chains.
I presume you mean that each car must have snow chains in the car,like the reflective jacket law.