1) The app is extremely well designed 2) There are some slick features that are virtually friction less to use such as telling the app to remind you about an email next week. 3) with #1 and #2 combined you have a more pleasant email experience than other clients.

All that being said, the problem with Mailbox as a standalone company is this: http://pandodaily.com/2013/02/11/wham-bam-thank-you-mailbox/

It's super fast and enticing to triage emails immediately rather than letting them gather dust in your inbox. Not much in the way of revolutionary features, but it definitely makes the entire workflow noticeably smoother.

As an iPhone user who has tried Mailbox, nothing.