Like for some others here, something feels off about the design. I think it's that the app feels a bit like an iOS app running natively on OS X: the icons on the left and at the bottom, the iOS mail app-style listing, and the tooltips that look reminiscent of the copy/paste menu. Not to say it's bad; it's just a somewhat confusing user experience, as if I'm running an iOS app with the Parallels like "unity mode" enab…
I think it's just going to take a bit of getting used to, and a bit more spit and polish from the author.