Simply open both backups in the app (you can even send them via AirDrop). The app will merge them into one. If it finds a conflict (like two bookmarks at the same place, or two markings that overlap), you can choose which version to keep. In the end, you have one merged backup which you can easily restore on your devices. The process - if done regularly - literally takes you seconds! Library Merger is still in its early stages and is being actively developed. The code is open source and can be found on GitHub. If you found a bug or have suggestions, feel free to contact me.