Product review (3 stars): Hard to rate - this filter is about 2 inches ...
Hard to rate - this filter is about 2 inches shorter than the original filter (didn't see other sizes, might've missed that) so it doesn't entirely wick water upward into the air column created by the fan. Evaporation is thus about 1/3 slower than normal.  Given that we have the 1 gallon humidifier, I can't imagine a smaller size exists, but  - we'll try to find the taller filter.