This was the first large SaaS project we had ever done but it was easy. We really didn't even have to think about it. It was essentially hit the Go button, come back when stuff is done, and check the error logs for any messages that could not be moved. I believe it was at least twice as fast as it would have been to move everything manually.
Engineering services firm easily migrates huge mailboxes from Gmail to Office 365 with minimal impact on users and IT