Product review (5 stars): Excellent
Excellent - enough so that it actually motivated my lazy self to write a review here (I'm also ordering another package now so was here anyway)

Ive tried a few different types of filters made by other companies and none have been as good as this one. Some, while appearing well made, didn't work well or really at all with my machine. Others were cheaply made - thin and flimsy - and weren't worth the money spent for the time gotten out of them.

These are thick, sturdy and well constructed. All of which means they last longer than the average replacement designs. If youve previously tried a variety of others, youll notice how substantial these are as soon as you take them out of the package.

--- Update ---

We run our humidifier 24/7 - probably around 22 hours a day on average, all week long.
Its been 5 weeks now and this filter is still working. Not as good as the first few weeks but still good enough to not change yet.

I use New York City tap water... not filtered and nothing added to the tank.
I flip the filter every time I refill the tank - which is around 3 times a day considering the constant use.
If the outer layer of the filter feels dry when refilling, I soak the filter in cold water for a few minutes (this usually starts happening after a few weeks of use). Ive never had more that the tips or portions of the outermost layer get dry.
Once a week I soak the filter in a mix of water and vinegar - roughly 1/2 cup of vinegar and 6 cups water - for 15-20 mins. Then rinse gently to flush the vinegar.
While soaking the filter I clean the machine tray - a quick scrub with soap and water, then a little bleach rinsed off thoroughly with cold water. The water tank too - soap and water, no bleach (make sure to clean the ring where the cap screws in, and the cap too).
The filter gets discolored with time, going from white to a light tan color, with a thin, slightly darker ring near each end - typical result of mineral deposits from what I can tell. I haven't seen anything like the dark and black mold issues people post pictures of online.

--- Update Two ---

Ive seen some people comment about black mold forming on their filter within a week of use. That much, that fast should not happen in a machine that is clean.

Assuming the tray and water container are being regularly cleaned... lift the top part of the machine off the water tray, flip it upside down, and take a look inside at the fan casing and motor. Black mold can form inside of the machine, and if this happens it will spread quickly to any filter you use - since it is already present and in close proximity to the filter. Wiping this area down will help prevent this - I used a tooth pick and disinfectant wipe to clean out the little grill at the center under the fan.