Good day all,
I wanted to update everyone regarding my experience with the factory-spec'd glass screen protector for the (original) VollaPhone.
While I had it on, I found it would accumulate prints / finger oils very easily, and to clean it, the best option was normal optical glass cleaner. Other cleaners, like Whoosh and/or Brillianize, didn't work as well -- those are meant more so for polycarbonate / plastic lenses. Once cleaned, the tactile response was best.
Sadly, in less than 6 months, the screen developed a long crack in it, extending across the top third of the phone's surface. Since then, more cracks, as well as several edge chips, appeared - I'm including several photos with this post to show the damage. I believe the cracks developed as a result of some bumps / drops of the phone (while in it's factory case), but was never sure how the edge-chips came about. As it was, I became tired of seeing the damage, and have now removed the screen protector (mercifully it came off in one piece, with the help of a microtool kit I have). The good news is that the original screen is undamaged, so the protector did it's job.
I'm now going to get some simple plastic screen covers (for the basic hardware, a Gigaset GS290), and replace them as needed. In my view, the glass screen protector will work well if the environment you use the phone is more 'light urban' than anything else.
Hope this helps everyone.