I'm seeing a very strange behaviour where some of the Insider features are available on one of my machine and not on the other.
One example being Modern Attachments. On one of my machines I'm getting the little triangle when clicking on Attach and then can choose whether I want to attach somethink local or from an online location. On another machine, very same account, OS version and Outlook version I'm getting the old experience where I'm only able to attach locally.
Also happens with the Google Preview Accounts. One one machine I was able to add my Google Account and Mail, Calendar and Contacts work just fine. On the other I can't get the correct popup to show up.