I received my Mailbox app invite today. My immediate impression upon using the app was that I needed a desktop version. I can understand some people might manage most of their email from their phone, but I spend most of my time on a computer.
I found the Mailbox way of dealing with email sorting to be an exciting option over the traditional folder-based system. Unfortunately, I would have liked access to my previous folders through the app, since I could not file those legacy emails in the Mailbox way.
I also am not a big fan of conversation view. I turn it off in my other email clients, and there is no way to do so through Mailbox app. This is problematic, because when I get an email related to an older conversation, it drags the rest of those messages into my inbox on other devices.
That being said, I am very excited about the future of email, and I think Orchestra did a great job in rethinking the process. I will wait for the next update or two to see if I will actually use this as my main email client.