I would be happy to explain to you the difference between the Newzik Essential plan, which is a one-time purchase, and the Newzik Premium subscription.
The Newzik Essentials offer is as a limited offer. Newzik Essentials lets you store up to 1000 pieces on the Newzik Cloud. You can store and manage your scores on all your devices connected to Newzik and use our Newzik Web platform on your computer. Of course you can take advantage of all our annotation features and organize your library as you wish. You can also have access to 1 collaborative Project to work with other musicians. However, Newzik Essentials will not give you access to Livescore conversions and exporting Midi and MusicXML files.
On the other hand, Newzik Premium would give you unlimited Cloud storage for your scores plus unlimited access to LiveScore conversions and to collaborative Projects. You would also be able to export MusicXML and MIDI files and to directly transpose all your PDF scores.