This script just adds one feature to Folders4Gmail.

When clicking on the parent label GMail will display all emails of descendant labels.

In other words, it will drill down and display everything from within that folders.

If you think a right-click option to show only emails with the same exact label would be helpful, let me know.

That being said I think the LabelLinks4Gmail script also does this, but with a different format and a few other features.