My first feedback to you is that the first contact is great thanks to the app's minimalism. It's really unobtrusive.

A second piece of feedback is that the menu bar icon looks poor on a retina display. I believe that one can use vector graphics (in PDF) or double the resolution (I always feel weird saying that, and want to say _quadruple_, but you know what I mean) to get a crisp rendering. I can screenshot what it looks like on my screen, if you have no opportunity to see it.