We had Radon testing done when we bought our house in Indy. It was built in the 1950's. Since it had a basement, our realtor recommended to have it done, so we added it as part of the inspection - we paid for it (rules might be different in your state but we footed the bill). They placed a device the size of a small microwave for ~48 hours prior to our inspection and it gave the readouts which was written into the inspection as a finding. Ended up finding crazy high levels and had the seller pay for a radon reduction system. They ended up attaching a cover to the sump pump that constantly runs and exhausts it outside the house. No issues since and I think they recommend rechecking every 5 years?
I don't know about the home tests