I would not be at all surprised to learn that both the commodity round and rectangular units use the exact same components inside. These surely must be made from jellybean off the shelf parts, and at similar price points to each other neither could possibly be assembled with much care or attention to detail.

I have a six pack of the rectangular ones from Jeff Bezos' Knockoff Whitebox Emporium. Even all sealed in the same container with each other, they all disagree by a spread of about 15%. I have no idea which of the six, if any, are actually producing an accurate number.

As an old toolmaker who might have dabbled in accuracy. I just shake my head when people complain about things like this because they think absolute accuracy --an impossibility-- is the important thing, (you can't afford anything close absolute accuracy), when it's repeatability that matters the most. Choose the one that repeats the best, toss the rest. Then learn what the "magic number" is that makes you happy to read and need to get the results you are looking for. Learn to apply some bloody "windage".

Remember: Rick Sanchez is a dumb-ass. And you only need to be 5% smarter than the tool you are using to be successful. So be smarter than the tool and understand the process.

because if it says anything other than 10% (the lowest thing it reads), then the dessicant needs to be refreshed.

it's more of a binary output rather than trying to look at 53 vs 55%

Mine work somewhat okayish, which is within the margin of error I need them for. I think there was one that was terrible though.

Mostly I use them for the temperature aspect, mostly for reminding me if it's too hot or cold in my room (because due to my autism, I often don't notice whether I'm at a comfortable temperature). I have a few scattered about my room and basically they act as a visual prompt to consciously ask myself if I'm at a comfortable temperature, and to act as a rough backup to whatever I'm feeling (because even when I'm consciously aware that my temperature is feeling Bad, I can't reliably tell whether I'm too hot or cold, so these terrible thermometers at least help me answer "should I get a blanket, or open a window?"

@Krauerking@lemy.lol Hygrometers are only as good as their components. Buying a DHT11/22 or SHT31 from AliExpress ($1-2) alongside an ESP8266/32 and you'd have much better results than buying these "are my cigars dry" pucks.