99% are scams. The 1% that are real are often "NFR" (Not for Resale) keys meant for reviewers. Using them violates the license.
There is no secret server generating valid license keys. That is a myth. Amp Free License Key
The interface is utilitarian. It is not "pretty" by modern standards; it resembles classic Winamp or older Windows applications. However, this simplicity allows for faster navigation once you learn the layout. It relies on menus and lists rather than flashy album art grids. 99% are scams