I just want to point out that the other device being compared actually includes a radon sensor and the cost of that device would be cheaper than the airgradient plus the radon sensor.
You can get a cheap analogue radon sensor. As others have pointed out, even if you do detect radon the typical solution is add ventilation.
Which is exactly what you do if you had a high CO2 reading.
Do you have any links to this? I’m very curious.
Just lookup radon test kit and how to deal with radon.