100% recommend a professional test and not just disposable things. They’ll set up a few machines on tripods for a few days and you’ll get to see highs/lows in different rooms instead of just a yes/no or a peak value. Can really help make a good decision about mitigation

Having kids made it a no-brainer

To my knowledge it’s global, not just specific areas, however the levels vary. In the Midwest (USA) it’s quite common to perform radon tests during a home sale, and homes with basements will frequently have a ‘radon mitigation’ system installed; basically a large fan draws the air out of the space beneath your concrete slab and air-tight plastic is installed in crawl spaces to form a negative pressure so the airborne radon is pulled out before it enters the home, and then exhausted up above the roof line to blow away like other exhaust from HVAC and appliances.

Have a system installed in my home to keep levels as low as possible, even though it tested below the ‘dangerous’ threshold when I purchased. (Better safe than sorry).