I hacked a few IKEA air quality sensors so, beyond their traffic-light color LEDs, they also log actual numeric measurements to Home Assistant. It's proving to be one of the more useful "ensmartiffication" for several reasons - including being able to check all the meters from one place on the go, and being able to position the device so its LED indicator isn't annoying my wife at night. But honestly, I wouldn't actually buy a smart device for this - soldering a NodeMCU into a cheap IKEA device is the sweet spot of relatively low skill required, and zero bullshit included.

I can't stand vendor apps. They're always garbage. In fact, the main reason I set up Home Assistant, and the main reason my wife embraced it and uses it daily, is because hooking up our A/C to it made it infinitely more useful than having it operated over the vendor shit app. With HA, either of us can reconfigure all A/Cs and then go and make tea or whatever, in time it took the official vendor app to fully open.

IoT is a disaster, Home Assistant and some tinkering is the only thing that makes it reasonable to have a smart device.