Product review (4 stars): Skuttle proves useful
In any other marketplace, this item is very difficult to find.  It seems that the humidifier manufacturer made a limited number of units, thereby making the replacement filter less popular.  I've been ordering this filter for the past few years via Amazon and it's made my life very easy.  The filter itself performs well (at least as well as I would expect), but the real value is in: a) that it's available, and b) that it arrives within a week.