When working in fullscreen view or with hidden Dock (thanks to MenuAndDockless for example) one maybe still want to be informed about new mails and if your happy with the stupid Dock badge you can now stop to read. All others who want to have a preview of new unread mails to quickly decide what to do without leaving the actual application should give my latest creation a try.
And YES, it is BETA,for Mail.app and the Inbox only and Mail.app needs to be running - would not make sense at all otherwise! And yes, there is a bug in Mail.app
