Product review (4 stars): ok
I've had my humidifier for 3 years and have been purchasing the genuine filters right here on Amazon.  I've always purchased directly from Amazon as the seller, as compared to a marketplace seller who may be substituting an aftermarket item instead (which is why the marketplace seller's price is cheaper- if it sounds too good to be true it probably is).

I've also been purchasing and using the Holmes S1708 Bacteriostat for Cool Mist Humidifiers which extends the life of the filter as these filters have gone up in price significantly over the years...