I've been using this app for quite some time, and, simply put, it is the Dog's bollocks.... the single search bar, no need to save a file, choice of external editor, markdwn., speed of execution, small memory footprint... the list is almost too long for such a simple app.
Not sure what has happened since my upgrade to El Capitan, but things are a little screwy WRT spell and grammer (heheh!) checking in US English. Can't quite put my finger on it, but it seems that the underlying changes made in El Cap. have degraded this apps otherwise excellent performance.
Here's hoping that the developer offers an update to the app in the near future.