Product review (5 stars): FAR BETTER Than The Original Honeywell Product!
Please note, this review is for the exact model/company as follows: UpStart Appliance Parts  2-Pack Replacement HAC-504 [see pic] This, I bought from the vendor named, Certified Battery, which is where I'll buy more from.

The first problem with the original HONEYWELL unit is it has a seam in it, which seems to fail first, by separating there sooner than it should! This one does not have a seam, so I think that is a big advantage. I am positive that this unit gets more moisture into the air, than the original also. With the original, I could never get more than a 31% reading on my hygrometer. On similar types of cold days, I get 36% with this.
I would strongly recommend the following for better health, and to get more life out of it:
1. Every day or two, remove from unit and flip it over. This evens out the wear, or pollutants that it traps while humidifying.
2. As another reviewer said, soak it in a 50/50 mix of water and cleaning vinegar for 20-60 minutes. Do this when it starts to get that crusty feel to it. Be gentle with it, because all of these are easily destroyed when wet.
3. I use a water add in solution form Walmart which is EXTREMELY CHEAP. Its about 4 bucks and is good for a couple hundred fillings.
Good luck, and Happy Humidifying!!  :-)
LOL