Important hints on Dropbox usage
As add-on feature the app supports the exchange of any kind of entries between devices via e-mail and dropbox upload/download. No matter whether the devices are owned by one or multiple persons collaborating, this feature allows you to use your own Dropbox or a shared Dropbox folder as clipboard for inter-device exchange.

This feature is not aiming to automate full synchronization between your own devices, but allows for manual selection and then automatically upload the contents to the storage cloud.

General hints:

Discussion about iCloud: Support for iCloud is still open as technical complications for users cannot be excluded. See especially this discussion by the Verge and the experiences of the Outbank App that supports iCloud, but since then ruined their reputation. Plus, many users want to exchange data also across platforms (Android, iOS) and between different users. Both use cases would not be supported with iCloud (iOS, single user only).