[nilkn]

I've used it for a while on my Android phone, and it's not even that polished. It's generally been somewhat buggy. In fact, until a week ago or so, the swipe gestures for archiving/scheduling were horribly broken on Android. The app still crashes sometimes or takes an abnormally long time to refresh after archiving an email.

I still use it because the combination of scheduling/archiving emails and auto-categorizing them as Focused or Other just works really well for my work email. I haven't found another approach to Inbox Zero for my work email that is this simple and effective.

I highly doubt it would cost Microsoft anywhere near $200M to build this themselves. I'm not sure what the motivation behind this purchase is. I'm not really loyal to the product at all, for instance. I'll switch the moment a more polished alternative comes out that has the same features.

[frandroid]

I'm not sure it occupies the same niche, but have you had a look at Google Inbox?

[nilkn]

I love Inbox and use it for my personal email, but my impression was that it can't work with Exchange accounts.