uHoo – most advanced air quality monitor, at least if consider a number of sensors. Including advanced sensor like CO, CO2, PM2.5, VOC, O3, NO2. And also traditional like temperature, humidity, and air pressure. Measurements look accurate enough.
The device does not have any local indicators. Not a single color LED to show air quality status. The only way it communicates with the world is Wi-Fi and mobile application. The application (v 3.8) or backend infrastructure that makes it work is unfortunately unstable. Also, an interface is poorly adapted to iPhone X.
uHoo is not portable due to many reasons like no local indication, no battery, need Wi-Fi (and new connection setup will take time).