I got migrated yesterday. Had to do the clear cache thing, but also had to clear cookies before it actually worked (Chrome browser).
Contrary to expectations, my inbuilt iOS mail app is still working. Connection from my full PC Outlook client is now broken though as informed. Another user on squadron has said his Office 365 App on Android has stopped working (deleted all his credentials) and currently hasn’t fixed it.
You can download Skype for Business from the web page, but not all the other Office 365 apps, which was about the only improvement I thought we might get - guess that didn’t come with the package.
I still hope there’s some way of hooking up the PC Outlook eventually, as that really was the best way of working with mail.