The idea behind KMoreTools was to point the user at external tools for a given job.
It provides a rather complex framework for that, including suggesting not-yet-installed tools.
The UX behind that isn't great though, which somewhat deep menu hierarchies and a somewhat arbitrary list of tools.
Most KDE apps have moved away from it, with only Dolphin remaining.
Instead provide direct integration with relevant KDE tools (Filelight, KDiskFree, KFind)
When kio-extras is not installed (or kcm_trash.so exists, but
is outdated) then opening the "Configure Dolphin..." settings dialog
will crash. It tries to load kcm_trash with its old KCModule plugin
construction signature and gets a fatal symbol mismatch.
kcm_trash was recently moved from kio to kio-extras and is
unconditionally loaded in non-Windows environments, so that
dependency should be required in the metadata for kdesrc-build.