What is the difference between firmware 'RST' and 'ALL' files?

The firmware with the .all suffix is the normal firmware file for upgrading. The previous configuration will be retained after the firmware upgrade.

The file with the .rst suffix is exactly the same firmware but with factory default settings for the router too.

Installing the RST file will both upgrade/reflash the firmware and reset the router back to its factory default settings. If you have a configuration backup for the unit it could then be applied to restore the previous configuration.

See the text file in the firmware zip for more information.