Optical measurement of CO2 with LED
To measure CO2 accurately you need to monitor the spectrum at 4300 nm AND monitor the spectrum at 3900 nm. The first spectral value gives you an indication of how much CO2 attenuates an optical signal that HAS to be reliably broadband in its spectrum. The second spectral value isn’t affected by CO2 hence, it can be used as a reference measurement should the “reliably broadband” light emission lower its intensity (due to temperature or ageing or other contamination in the signal path).

So, ask yourself; does the circuit/module you have uncovered do what I have described above or, does it do it cheaply and with subsequent inaccuracy?