I put the Ikea Thread sensor in my fridge a while back and it's been a lot more useful than I expected. My fridge had been periodically getting too cold or too hot, I suspect the issue is that the captive touch buttons that control the temp get occasionally bumped, changing the set temperature. With the thread sensor I can have Home Assistant send me an alert when the fridge leaves the safe zone for too long so I can manually correct it.

It's also been interesting to see when placing hot food in the fridge how long the temperature stays elevated for. I put the sensor in a ziplock bag and sucked the air out of it so it has weatherproofing.