Review on Temtop LKC 1000S: Accurate Formaldehyde Pollution & Temperature Detector by Tay Fair

My rating has been changed from 1 star to 2 stars. I've found the PM2.5 readings to be fairly accurate for the device I have. However, inaccurate PM10 readings (as detailed below) are a serious drawback. This is one of those moments where I wonder how a product gets such good reviews. The PM10 reading is always about 1.4 times the PM2.5 reading (as another reviewer also pointed out). He hardly differs from the coefficient 1.4. The readings I'm getting (outdoors) with this meter are pretty close to local air quality readings for PM2.5, but TOO LOW for PM10. A low PM10 value gives a very low AQI. What's going on here? The accuracy of the temperature and humidity measurements doesn't look very good either. I'm interested in reading other parameters that I can't easily check (HCHO and TVOC)! Update: I had a rather unsatisfactory interaction with the seller. If I understand their Chinese, they insist that there is a direct relationship between PM2.5 and PM10 ratios. It is not true. Please note that there are no accuracy specifications for this device and the seller cannot or will not provide any accuracy claims. It turns out that the recording function only works for PM2.5 and HCHO. The recording function does not work for PM10, TVOC or AQI. Second update: I've tested several of these so-called air quality meters and none of them seem to give correct particulate matter readings. This works really well with PM2.5. I'm still having a hard time determining if the HCHO/TVOC readings are accurate. Outdoor HCHO/TVOC readings are slightly lower than indoors, which makes sense. The accuracy of the temperature and humidity measurements is not that great.