I think if you use at least a stick of butter a week you'll be fine w/ the butter bell. It is also sensitive to the outside temperature so in essence the less humidity and heat in the air the longer the butter will remain wholesome. This probably explains why it lasts 5 days for some and 4 weeks for another.
The design and science behind it is simple so you can get one made by Tremain, or Crate + Barrel or BBB or Sur La Table.....wouldn't be surprised if they were all made by the same company.
To answer your first question, no I don't have one prolly because I don't use that much butter any more and of course there is the counter space (or lack there of) for me to consider. When I need rm temp butter fast I just grate it.