Update bottom of post
This arrived this morning, a few weeks after ordering it. It’s a metal replacement backplate for the iphone 4, likely in reply to the concerns of the glass back succumbing to scratches and possible shattering.
Wired’s review of the metal replacement back plate.
My preference is the slip in pouch style, the one I have is from proporta. These cases are reportedly responsible for the scratching on the glass back. Indeed, I have 2 nasty full length scratches on mine, likely from the proporta case. Therefore Apple have so far removed all these styles of cases from their stores.
So the answer was to order this replacement backplate so that I can revert back to the proporta case. I will still add a protective film over it, as it will still get scratch, but it feels more solid and should not be at risk of shattering like the original glass back. And frankly, I feel I will prefer this brushed metal back more, once I have fitted it that is.
I have now replaced the glass back with the replacement and it was just stupidly easy. Took no more than 4 mins to do. All you need is a Philips #00 screwdriver, undo two screws, slide of back cover and slide on replacement.