Not sure you will like my idea , but here is what works for me. I got the Defender case for my M8, the same day I got the phone, at the beginning of last April. I hated that dust/moisture would collect between the screen and that plastic protector, so I gently removed that piece from Otter box, just 2 days later. The Gorilla Glass is tough and I have not scratched it in all this time. And yes, I'm kinda rough on stuff. I've dropped it off my belt a couple times getting out of my semi (about 5 or 6 foot drop) case works good for that. That screen cover is just waiting to get sand or salt or some other abrasive trapped between it and the screen. I say remove the screen thing. It will just push out with a little effort. Make sure to scrape any remaining glue off of the frame of the Defender, so it does scratch your phone.
Posted from my HTC ONE M8 via the Android Central App