For example, the two sensors I have right now, with the windows open, the S8s report 478 and 455 ppm of CO2, while the SGP30s report 400 and 405 respectively. Without having calibrated instruments it's hard to know if any of these values are good, but they seem at least not too wildly off.
The SGP30 is a lot more compact and much less of an energy pig than the S8; the S8 will actually take so much current on the 5V rail that it'll cause the voltage to sag if you're powering it through USB with other devices connected (https://blog.jean-francois.im/2021/05/08/building-a-simple-a...). It's also a lot cheaper.
However, the SGP30 approximation can be off by a bit, and the calculation of the humidity value to give the sensor is a bit gnarly (https://github.com/jfim/air-quality-monitor-firmware/blob/ma...). It's also pretty obvious that the SGP30 has a hardcoded floor of 400 ppm CO2eq and that it won't ever return a value lower than that.
Is using H2 to detect CO2 "good enough" for all non life-or-death situations?
Edit: And to clarify, I was mainly asking the parent comment as to what is their application that demand NDIR or "more direct" CO2 sensors.
[1] https://www.sensirion.com/fileadmin/user_upload/customers/se... [2] https://rmtplusstoragesenseair.blob.core.windows.net/docs/pu...