Great, but lacks some flexibility Rated 4 out of 5 stars
After development of gmail manager seems to have stopped, this is the only extension that seems to give me a similar usability.
It does things a bit differently, but I have quickly come to terms with this, though I still miss the option to click the icon once to login, and a second time (when I'm logged in) to open up the gmail inbox in a tab. I have to look in sub menus in order to open up the inbox.
The settings doesn't give me a choice to change the behaviour to the description I gave, and this is what makes Gmail Checker get 4/5 stars.
All in all an otherwise great extension with both its simplicity being one of its strengths but at the same time causing it to fall short on flexibility.