Visuals and animations are infinitely easier to get "looking right" when you can modify parameters directly in a running app via REPL. That's possible with RubyMotion. In particular, check out https://github.com/rubymotion/sugarcube#repl-view-adjustment... .
I second this. I demoed the Sugarcube repl for our mobile team (I'm primarily a JavaScript dev who has fallen in love with RM) and everyone was universally blown away. It's the most useful thing ever -- well that, combined with Teacup.