The trial version is fully functional for your local (not published online) websites. You are free to use it for testing or development purposes. You are not allowed to use it inside distributable implementations (such as demos, applications or CD-based webs).
Purchasing Likno Drop-Down Menu Trees entitles you to use the code in your publised website online.
Apart from the features above you also get benefits such as:
Upgrades: All minor updates of the program are for free.
Support: Quick and thorough answers from our dedicated support team plus detailed documentation.
Not to mention that you would be contributing to Likno Drop-Down Menu Trees's growth as the registration fee is invested in its rapid development. More powerful features will be available to you.