After using it for two days, I have to revert my positiv reply.
The Co2 readings are 190ppm off and cannot be calibrated. I even left the unit outside for a day, hoping it would calibrate around 400ppm, restartet it several times, hoping it to calibrate, but it stayed aroung 590ppm.
The air quality LED is really bright and can not be dimmed, only off/on. Its way to bright for a bedroom at night, lighting up the whole room.
Also, a backlight is missing badly. There is no way to read the display at dim light. This makes it pretty useless in dim rooms, especially because the bright led blinds you at the same time.
I also noticed, when temperature comes down to the freezing point, it does not display the real temperature anymore. but only ‘LL’ which I guess means low.
I regret I bought it now and wasted the 50 on it.