[Qingping AQ monitor](Limited-time deal: Qingping Air Quality Monitor, Indoor Air Quality Meter Detects PM2.5, Temperature, CO2, and Humidity, Smart Air Quality Sensor for Bedroom, A Rechargeable Device with 2 Colors, Smart Home https://a.co/d/3ESHdmV) (Xiaomi Cleargrass sensor) which is on sale right now for less than I paid 
Simple to use interface and a nice reference for each level the user can easily refer too right from its touch screen. Easy to glance at its screen and see color indicators when levels are above normal ranges. Accuracte in comparison to an Airthings sensor according to another user 
Doesn’t directly interface with HE, but it was very easy to integrate with Home Assistant. Using very simple automations on HA, I can trigger virtual switches on HE using @jason0x43 ’s HE to HA integration when levels are outside of a healthy range.
