Is the outlook plugin compatible with outlook for mac?
No, sadly it's not. What we have in the Mac is a Thunderbird and Postbox plug-in. Vote for it here: https://todoist.com/Vote/show/6381/.
When will you have an outlook for Mac plugin? The application is pretty useless without it. I paid for Premium and found out later that the outlook plugin did not work for Mac.
We do not have any kind of ETA at this time, but it is something we hope to support at some point.