This post is more or less an observation and it might or it might not be relevant. In short when status bar is set to ON and i am adding some QActions to global toolbars. After when the workbench switches i get some flickering. Part of the tool buttons from left to the clicked button flickers. This behaviour isn't noticed if status bar is set to OFF. I think i did found a way to do what i want (TabBar) without much flickering involved. Will need to do more tests for the final confirmation. Quick search in FreeCAD master does seem to indicate toolbar (tool buttons) flickering when changing workbench was an issue in the past and was resolved by some workarounds.
Therefore what i didn't see noted and i decided to write it down here is it looks like status bar status set to ON/OFF seems to affects the toolbar flickering behaviour.