We use a butter bell, works great. For those who mentioned the water going bad, just add salt, keeps the water fresh for a long time.
You really don't need it, we just have one so we use it. It keeps the cats out of the butter, but that wasn't a serious problem anyway. It keeps the surface of the butter nice and "fresh", if a stick is left out on a plate after a while the unused sides start to look a bit dark and less appetizing. Not a real problem, just nice to always have fresh looking butter, and at times the butter got so old looking after a week or so we threw it, it can go much longer in the bell and it looks fresh.
Anyway, yes we use one and like it, no it's not needed but I do like the utility of it. We have a hand made bell that looks very nice out on the counter, I really like that aspect as well. Not a big deal either way. Maybe slightly more work to pack it in, add water and salt, etc. But really not enough work either way to worry about.