Gerard; To answer your clarification question. When you gain more control over your diaphragm, you’ll be able to sound the notes while drawing in less air, or vice-versa as the situation demands and thus balance the breath and keep playing. If there is currently a large difference in volume between the blow and draw, you may be playing to loud… if so, try playing a little quieter and as you gain more breath control things should really start to sound nice.
Re: The bad habit question… here your both right 🙂 Breathing out over the harp is a cool technique to expel excess air when playing in general, especially with chords and in between phrases, so the concept it self is not a bad habit, however using this idea with the laughing clown would not be a good idea, and would indeed develop a bad habit. You want any single note playing to be clean, especially when starting out.
In general I’d say to keep your single notes clear, try feeling your diaphragm as you play and only play the exercise for as long as is comfortable, even 20 seconds at a time is great.
I hope that clears thing up a little!