But can I sort my unread emails by ascending date? If I'm practicing inbox-zero, I don't want to fight my email client to review my oldest (unread) emails first.
It seems to sort with the newest at the top. The app is free so try it out. It took a little getting used to after having used Mailbox for so long, but it unquestionably better.
I don't know about desktop. I just use my phone/ipad for 90% of my email, so that works fine by me.
As for being hired, Readdle makes a ton of ios apps, and are profitable in their own right. Also, while Spark is free, some of the features they've hinted to as coming in the future will likely be in-app purchases / upgrades, that will allow it to be profitable as well.
Spark by Readdle has taken up slack there, and they look like they're building it in a way that will actually be monetizable.