Product review (4 stars): I think you're supposed to change them before that but it didn't seem like it needed changed so I left it go
I bought this to replace the original filter on my "Honeywell QuietCare 9-Gallon Output Console Humidifier with Air Washing Technology, HCM-6009". This filter is not an exact replacement (I believe it specifies that though). The filter that came with my Humidifier was blue on one side, not sure what the differences are though. This replacement does seem a little shorter (2 inches at most) but I don't see that as a problem.

The first thing I noticed is this filter seems to draw water through the entire filter. While the fan was off, it took about 15 minutes for the entire filter to be wet. The original blue filter never seemed to be wet past the bottom 3" regardless of if the fan was on or not. Both filters humidified my house but this one seems faster, most likely because more surface area of the filter is wet.

My old filter lasted about 4 months. I think you're supposed to change them before that but it didn't seem like it needed changed so I left it go. I've only had this filter a few days so I can't say how long it will last. I keep my humidity between 45%-55% so I really only need to run this 3-5 months a year. I'm hoping to only need to change the filter once every 1.5 seasons.