I foolishly bought one off the top of the best-seller list at Amazon a couple years ago. It was like $35 and came with a little card that said "Hey, if you give us a 5 star review and send proof to SHADY_EMAIL_ADDRESS@gmail we'll give you a $25 Amazon gift card!"

It did work reasonably well, but if you failed to clean it and fully dry it out within 6 hours of using it, it would get an INSANE mildew smell.

Amazon of course didn't bother to do anything about the company when I tried to report them, and they seem to have disappeared/rebranded since then

What were you expecting? They can't fundamentally change what happens when you leave things wet for hours.

My teakettle is moist for hours, some of my dishes are moist for hours, they don't smell like mildew. I'm in the bone dry south bay in a warm house

My guess is water is getting trapped somewhere in the device's Chinesium crevices, or maybe they found a way to make plastic cheaper by making it susceptible to mold.

Every cool-mist humidifier has this problem. Use one of the Vicks vaporizers that boils the water if you don't want to deal with it.

Ours just runs until dry. Pretty sure it’s ultrasonic but it’s cheap and there’s never been a smell. Those are the joys of living someplace you really need a humidifier. Water just disappears.

not the problem you're trying to solve but there's an additive called "humidifier bacteriostatic treatment" that could help with the smell

You have to add bleach or humidistat to evaporative ones or keep them running full time. You also have to replace the media once a month or so. The steam ones are better imho.

I prefer steam for less cleaning too, but they're power hungry.

I wonder if the old 10% hydrogen peroxide trick would fix that.

One of the major issues with humidifier design is that whatever you put into the humidifier gets into the air, which sounds obvious but is an issue. We don't want to use chemicals to keep the paper wick from getting moldy because then we are breathing that. Or with ultrasonic they throw up mineral dust into the air. We end up just buying a lot of paper wicks.

Yeah, but those are functional limitations, not failure to function.

Ultrasonic is fail by definition. It's not hygienic and emits minerals.