Not sure about air purifier, but I have a Midea dehumidifier and it publishes runtime and setpoint info I pull into Home Assistant along with power draw from a smart plug. I can see how often it's running at different times of the year and how much it costs. Ended up saving some money tweaking it from 50 to 55 after seeing runtime and A/B testing both.

Also auto on/off. If you put Home Assistant app on your phone, you can wire up automations that turn things on and off depending on whether or not you're home. Could also have Home Assistant pull in air quality/pollution info for auto on/off. High pollen count today? Keep it running so I sleep well. Low pollen count? Turn it off.

Maintenance is minimal. I set the dehumidifer up 2 years ago and haven't touched it since or had a single issue. Main thing is a) get it working, b) get it isolated from internet, c) never touch or patch it.

Once the data is in Home Assistant, I can also look for correlation with wearable health info. Does purifier running improve sleep? Does changing thermostat set point improve sleep?