Pros
Atlassian is best company I have ever worked for, and I can't believe the amazing projects that I have been able to work on. In my two years at Atlassian, I have been able to achieve more at Atlassian than in my entire career. And I am constantly pushed outside of my comfort zone (but I think that's kind of fun). It's not the kind of place that your hand will be held, so it's really up to you to thrive and succeed. It is a company where the values are lived, and employees are really encouraged to be the change they seek.
Cons
Sometimes the work-life balance has been tipped too much on the work side. Silo's have started to form in the organization, and I think the M-team can address this by communicating across functions in a more effective manner.