A passport cover is more investment than mere purchase. It stops the edges of your passport from becoming tatty, and that's key because a tatty passport doesn't encourage a check-in clerk to deliver the felicitous phrase, "We'd like to offer you an upgrade." Whichever you chose, make sure it's in a vivid colour. You don't want to be ages peering into the dark recesses of your bag as the clerk's smile grows strained. Therein lies a seat in the rear by the loos.