Technically, no. Currently this plugin just creates a custom sidebar widget area for each page on which you’d like one.
The idea with “Add to sidebar rather than replace” is this:
When you check the box to add a page-specific sidebar, the plugin automatically creates a corresponding widget area under Appearance/Widgets.
If you check the “Add to sidebar rather than replace” box, what should happen, is that whatever widgets you add to the newly-created corresponding widget area (again under Appearance/Widgets) will appear in addition to the existing sidebar.
If you want to have one sidebar that you apply to many pages, you might consider creating a custom template for the pages on which you’d like the common sidebar.
For example, if you had an About page on your site and you have three sub-pages like: