Product review (4 stars): expensive but the humidifier works well for 5 winters so far...
these things are expensive for what they are (stacks of filter paper that are hot-glued).

seems like they used to work longer before smelling bad, the last few batches of these don't work nearly as long.  and I'm unwilling to use the toxic water treatment chemicals that keep these aseptic longer.

still, my humidifier (which uses these filters) has been going strong for 5 years, and I typically use 2-3 sets of these filters a season (depends on the winter!).  The humidifier works well and keeps us comfortable.

So a four star for these filters...