Lochkamera for OS X - El Capitan & iOS lets you apply subtle, film-like filters to your pictures.
It is meant to competely integrate into your Apple Photos workflow. The recommended way of using the OS X app is via the Photos extension.
On iOS you can use both the App or the Photos Extension, and you will always be working directly with your photo library. No importing/exporting and duplicate photos.
All your photos and edits can be synced via iCloud Photo Library, and all edits can be reversed.