What's the difference between a radon-only monitor and a multi-sensor air quality monitor?

Radon-only units like the Ecosense RadonEye and Airthings Wave Radon focus on radon plus basic humidity/temperature. Multi-sensor models like the Airthings View Plus and Wave Plus add CO2, VOC, particulate matter (PM) and pressure sensors, so they double as whole-home air quality monitors at a higher price.