The basic features of Duplicate Scorer are free. You can use them for as long as you like without the need to register the application or buy a licence.
Basic pairs and individual competition scoring will always be free in all future versions.
A licence is only necessary for Advanced Features. Even then, you should not buy a licence until you have tried out the Advanced Features. Even without a licence you can use the Advanced Features free for thirty days, to check that you like them before parting with any money.
See the Features menu to discover what is included in the, free, basic features, and what extra Advanced features you get if you purchase a licence.