I have always left one stick of butter out on the counter, in a regular old butter dish.
I probably use it up within a week, and I have never had it go rancid. My mom does the same thing.
I bought a butterbell recently, but haven't tried it with the water in it yet. In the wintertime, my kitchen is so cold sometimes the butter is too hard even sitting out on the counter!
I do use salted butter, and I don't know how unsalted would hold up.
I just haven't been the same
since that house fell on my sister.