I was curious about an air quality monitor. Without much research I bought one on Amazon branded Khaco Tuya.
It claimed to have 6 sensors: PM2.5/Formaldehyde/TVOC/CO2/Temperature/Humidity.
Unfortunately when I received it I found issues. The sensor frequency is much too high and makes Home Assistant dashboards slow to use if they try to graph it’s data. Worse yet is the fact that the CO2 reading is nonsense, it just jumps from ~200 straight to 40,000~ and back again constantly. The pm25/formaldehyd/voc all seem to track each other which look as if they are a single sensor. The temp/humidity seem okay.
If I was to look again I would read through more discussions such as on Reddit to find a quality device.
I took some pictures of the internals if of any interest to anyone.
ZT3L Tuya module:
AHT 20 Temp and Humidity sensor:
The PM2.5 sensor looks very similar to a Sharp GP2Y1051AU0F although pictures I find online have more holes in the metal cover.
The PCB does not fit well in the case and has a continuous pending force on it: