The extensions are third party softwares. Try to ask the author if there is not Help or description (and there is link to the autor's site) at the extension download page.
The download page gives you many informations:
https://extensions.openoffice.org/en/...
From the download page:
"After installation, a tool bar will appear with 4 buttons for 'Readability Report', 'Brain Overload Report', 'Cohesion Report' and 'Detailed Report'. If it is not there, select View from the menu bar, then Toolbars and 'Add-On 1'."
I suppose that if the buttons are not appeared then this extension is not compatibile with the newer LO versions or with the installed Java. Otherwise the extension has newer versions: 2.x.x, but they marked as "compatible with LO 3.x versions". Those LO version are very obsolete today.