Ultimate Updater 5.1 Beta 1

This Beta refresh fixes branch handling discovered immediately after the first 5.1 Beta publication.

Fixed

• update beta -up is now supported.
• update -up correctly stays on the configured beta branch.
• USED_BRANCH="beta" is preserved.
• Beta no longer redirects to develop.
• Version checks, help output and branch handling support master, beta and develop.
• Beta installation and update documentation now points to the active beta branch.

The functional 5.1 Beta feature set is otherwise unchanged.

Beta software should be used with current backups.