TPE 3D focusses on providing a 3D model of the real world topography so you can see how the light will fall on the land. It de-emphasize numbers (e.g. azimuth, altitude) in favor of the visual elements.
TPE for iOS presents all the facts and figures you will need about the sun, moon and Milky Way. It includes a variety of map types (5 in total at the time of writing), and a number of additional tools such as Visual Search, Shadow length calculation, distance to the horizon, celestial events, and, of course, Skyfire.
We expect to maintain both apps for the foreseeable future: they each serve slightly different needs and use cases.