I just installed an IQShield screen protector on my F6x. The IQShield is a plastic film with a wet application. The product comes with six protectors and good instructions on how to apply. I was very happy with the IQShield on my old F3, so I thought I would try it on my F6x Sapphire.
I am happy to say that I can't even tell the screen protector is on. I meant to take before and after pictures, but I forgot. Suffice it to say that I would defy anyone without a magnifying glass to even know it was there.