Product review (3 stars): Filters work great--but this style humidifier = costly consumables!
If you are buying, I feel your pain. These filters, and all filters for this style humidifier, only last ~ 1 week after initial use. This isn't the filter's fault, but simply a result of the design style. At ~$8 per filter, you'll quickly pay more in filters than the cost of a different style humidifier.

This is the classic death by consumables model: 'cheap printer; printers cartridges made of unicorn blood'. I'd recommend making the jump to something else.