Just to add a little note from my recent experience installing as a service, in macOS Mojave (10.14), it may be necessary, depending on what you’re backing up, to add Duplicati.app into the “Full Disk Access” folder under System Preferences --> Security & Privacy --> Privacy. For me, Duplicati didn’t have access to some important folders (like ~/Library/Mail).
To install, I followed this fellow’s instructions (minus the Homebrew installation – I just installed Mono from the project’s site), and it’s working well.
Performance-wise, the initial backup of 1TB to a local USB3 non-SSD drive (using encryption) on an i7 Macbook Pro with 16GB of RAM took about 16 hours. Subsequent runs take around 20 minutes with the “counting” process, etc. I’m not sure if that’s good or bad.
Thanks,
Mike