Zagg's InvisibleShield was just unbearable to install. Installation of a screen protector should be an overall easy task.
But finally I'm done applying it and I'm not impressed. Days go by and the transparent layer seems to have already been penetrated by something, perhaps my keys in my pockets. It's disappointing for something meant to be a scratch protector. I observed that simple impacts and small concussion with blunt to moderately sharp objects can penetrate the so called "shield" as though nothing was even there. The so called "shield" is of poor quality, and certainly not of good use. Coupled with the frustrating installation process, I conclude that it's not worth it.
Another screen protector, Gadgetshieldz, was quite simple to install and turned to actually be a good shield against scratches.