The professional version of Arpeggionome, Arpeggionome Pro puts all the details in your hands. You can change the key, step distance, octave style, tempo, and numerous other musical and technical settings. The ability to save and playback patterns can help with consistency, and the integrated iTunes file sharing makes backing up and transferring files painless. The Pro version is $14.99 and Arpeggionome is $4.99. Compare the features list to see which is right for you.
You can read more about this new release here: http://www.idesignsound.com/alexandernaut-releases-arpeggionome-pro-a-new-midi-controller-for-the-ipad/