Interesting observation. I never thought about that... I suppose it would indicate some form of air tightness quality. And yes, it is normal to use your air valve button with your left palm, not your thumb.

After further experience, I'm not sure my observations are entirely accurate. The Gabbanelli is much more efficient in the amount of bellow movement required to play it and the reed respose is quicker. The real advantage seems to be the ability to quickly take in more air on a pull note without affecting the tone quality and it doesn't require a full depression of the air hole, only a quick press of the button. An interesting subtlety of technique in playing.

All of this is probably just the process of getting to know a new box and the small variables each one has.