I was not expecting much ordering

Pros
- 3000 mAh battery ( 10 hours of battery life)
- additional sensors (VOC, PM2.5)
- correct t, RH and CO2 measurements (not sure about other)
- 16 different screens including trends
- Active airflow with the relatively quiet fan
- quality design and schematic inside (no glues, connectors, replaceable sensors)
- good CO2 sensor inside – SenseAir S8 LP
Cons
- slow charging – 8 hours (in operation mode)
- no connectivity (Bluetooth, wi-fi, USB mass storage) – nothing
- no ambient light sensor
- unconfigurable high CO2 limits (GOOD is up to 1000 ppm)
See device insides: https://wiki.liutyi.info/display/CO2/K6+Inside
Price: ~100$ (sale price was 83$)