I don't know because it doesn't seem to be in stock anywhere yet. (An odd mistake on Apple's part, as you certainly want all the accessories to arrive on the day that people buy their phone, otherwise they're much less likely to buy them).
With it on, the glass is separated from flat surfaces you set the phone on, and the phone looks less distinctive too (which can be a good thing).
I took a ziploc bag folded in half (therefore 4-ply) and wrapped it around the metal, and no matter how hard I squeeze it or cover it, the signal doesn't drop below 5 bars.