Kopia is the strongest free, open-source backup tool that also ships a GUI. It does deduplication, compression, client-side encryption, snapshots, and retention policies, and it runs on Windows, macOS, and Linux. Unlike restic, you don't have to live in a terminal to use it.
So this comparison isn't “GUI vs. no GUI.” It's about how much flexibility and how many concepts you want between you and a working backup. Kopia exposes its engine; BackupKit hides it.