I'm Karl Traunmüller, developer of Computable.
I don't want to advertise my product here, just post a few clarifying words. Computable is built around IPython's notebook metaphor, so it's something rather different to Pythonista's IDE approach. Just like Roger said, I see more than enough room for both apps.
By the way, I have Pythonista on my iPad, and it's a gorgeous app, very well done.