Think it works like this:
You equip it, get the bless bonus from it. the bonus is based on eval int, if you have 0 its like 1 str/int/dex, if you got 120 its like 12 str/int/dex
you unequip it you lose the bonus. equip it again and it use another bless bonus. if you wear it all the time it will use a new charge every now and then.
at 0 bless charges its still a sash, but no bonus from it.
If only it could be recharged somehow
In terms of value; If I dig through my stuff im sure i can find one or 5, its like invis items/teleport jewlery, its alot around. Good cleanup value though