I don't get this. My current air purifier (philips) costs like 150€, includes an air quality sensor and the app reports shows graphs with PPM, VOC, whatever. Why would I pay double for a device that doesn't even filter the air of my room?
different use cases. I don't expect you to go around with your air purifier attached to your neck :)
Sure but same tech. It'll boil down to economies of scale.
Also indoor AQ where you spend most of your time is more useful to know. Dust and CO2 are something you can actively reduce.