While the source uses the plow function to determinate whether the button should be visible, the compiled code always just returns true.
Using the button when it is not really enabled, throws an exception.
I installed and built the plugin locally and the compiled code changes to what I would expect, so I think the repository code is out of date.
However since dependencies aren't locked, I'm hesitant to just PR a new build, as some other neos-ui-extensibility might break something for older neos installations?