Product review (4 stars): Pretty good!
I have tried several types of replacement filters for the Honeywell humidifier, and these appear to be decent. They are even slightly better than the filter that came with the machine. How long they last depends on what speed you run the humidifier on. It is important to flip the filter every time the water is changed, which should be at least daily. Should it dry out, rinse the entire filter. No filter will last as long if  you don't keep it wet, and I can get about four weeks use out of these.