For which use cases it is better than bluetoothctl linux utility?

Ha-ha! Most of people thins that syncspirit UI is terrible :)

Well, yep. For now the positive differences are

• better speed transfers (up to x7 speed up on my setup).
• different UI (including unique features like see in realtime tree-like structure of remote/local folders).
• Windows XP support
• it targeted for long-awaited “selective sync” mega-feature (asked for many years by syncthing users; but it is out of scope of syncthing business, so, it will unlikely be developed). I plan to do it after 1-2 releases (after implementing “ignoring local files” feature).