Excellent, because it's not only a way to open OR to switch to the Gmail tab (it's very useful when it's already open to avoid opening several Gmail tabs, by using the addon icon, and it opens as a pinned tab, that's a great idea.). It's also a Gmail badge counting the unread messages. The check messages every X minutes is great.

The feature that is missing for me, is to count new messages from now (because I've some messages that I've let unread in Gmail on purpose, like spam, or for other reasons). Customizing the unread badge would be a great idea also. It's too small.