When comparing DockbarX vs Plasma Kickoff, the Slant community recommends DockbarX for most people. In the question“What are the best app launchers for UNIX-like systems?” DockbarX is ranked 10th while Plasma Kickoff is ranked 18th. The most important reason people chose DockbarX is:
DockbarX has an available plugin called "DockBarX Xfce4 Panel plugin" that allows DockbarX to blend in seamlessly with the XFCE4 panel, which is great for XFCE users due to the limited options of the default panel.
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Pros
Pro Great plugin to help blend in to XFCE4 panel
DockbarX has an available plugin called "DockBarX Xfce4 Panel plugin" that allows DockbarX to blend in seamlessly with the XFCE4 panel, which is great for XFCE users due to the limited options of the default panel.
Pro Easily customized
DockbarX has inbuilt settings that allow the user to easily customize the look of the dock, from changing the text color to the background color.
Pro Easily the best Win 7 taskbar functionality
If you want a combined launcher/manager, a la Win 7, this is it.
Pro Visual design is good
Pro Decent default with good customization
Pro Has different options and full customisation of the KDE desktop
Cons
Con Not actively updated
Less than a dozen updates since 2014: https://github.com/M7S/dockbarx/commits/master
Con Lacks more extensive taskrunner launcher capabilities
No plugins, etc.