nefiwashere, I have the Zagginvisishield on my iPad since I first bought this iPad (June 2010). I cannot really tell you the difference between not having it and having it-->since I have always had it. I can tell it is on my iPad. I have an iPad2 and for it I used a 3M shield (US$10.00). Compared to that shield, the Zagg product is superior. The Zagg is easier to clean and keep clean. I cannot tell if either iPads' responsiveness is reduced by either shield. I have compared my iPads with a friend's iPad screen--he doesn't think shields are necessary. His iPad, once cleaned, didn't show any scratches or wear spots. So he might be right about not needing shields.
It just boils down to my peace of mind and the what-ifs...what if I didn't have a shield on my iPad and....a cat started pawing it? What if my friend (with long painted nails) wanted to use my iPad...what if....in any scenario that could potentially scratch my iPad, I would rather have a screen on it and have it be scratched.
The Zagg HD isn't available until after March 14, 2012. So you probably won't get any responses to your note until after that time.