If you want to make measuring CO2 your obsessive compulsion then sure, buy a lab grade instrument. If you want to get a practical reading of the air quality that is more than good enough, affordable, and looks nice on your bedside, the ikea one is a great option.

The outdoor CO2 is rising every year. It is not fixed at 400 ppm.

But close enough for most purposes. We aren’t doing laboratory measurements here, I just want to know whether or not to open a window.