Does it support multiple people editing the same document at the same time?
We chose them, having heard terrible things about Google's support (or rather, lack of it). Having experienced Microsoft's support, we are now surprisingly close to switching to Google on the basis that it can't possibly be worse.
Here is a fun thing with Office365. Let's say you want not just to edit a document concurrently, but to see everybody's changes. It doesn't work right in Word online:
https://support.office.com/en-us/article/Can-I-use-Track-Cha...
I was pretty shocked to learn this. Although it seems calculated to cause you to buy a premium license, so I suppose I shouldn't be.