I would rather prefer an app which gives me an option to sync via a service of my choice (at least some well established ones) e.g. Dropbox, Netxcloud, maybe for someone it could be even Google Drive, or their own sync if they have e2ee. etc.

> syncs to iOS

It just an OS so I would put it as "is available on OS"

> but not via iCloud

But the sync options are not limited to iCloud.