I think it's a fine tool if you know the basics and need to pick up a new language quick, but I'm not so sure it's right for beginners. I'm open to counter arguments.
  1. It obscures original error messages
  2. It tells you that passing code failed because you missed the exclamation point at the end of "Hello World!"
    And other such nonsense
  3. It delays beginners from setting up their own development environments
  4. There is no interactive shell you can use for experimentation