If you own the vehicle and the radio came with the car, you have a legal right to unlock your own property. However, selling the code calculator or using it to unlock stolen radios is illegal under the DMCA (in the US) and similar global laws regarding circumvention of anti-theft devices.
However, there is a notorious problem that plagues these units: audi rnse code calculator
Just remember: treat the code carefully. One wrong digit, and you are locked out for an hour. Three wrong digits, and you need professional help. If you own the vehicle and the radio