Thank you for your question! The main difference is that the Unity version includes an example scene demonstrating how the tiles can be used, along with a variety of prefabs that are ready to drop directly into your project. It also comes with the water shader shown in the video, plus some simple UI elements and icons used in the demo. But I would say the main reason to go with the Unity version is the bonus example scene.
If you’re working in another engine, or you don’t need the example scene, the Itch.io version is likely the best choice. It’s more affordable and contains all the core graphics as PNG files, giving you full flexibility to use them however you like.