Sparkle 2 adds support for application sandboxing, custom user interfaces, updating external bundles, and a more modern architecture which includes faster and more reliable installs.
This has been many years in the making.
Moves extraction, validation, and installation into a submitted launchd agent/daemon with XPC communication
Adoption of improved atomic-safe updates leveraging APFS
[Lots of work in there…]
Source: Michael Tsai