I'm in my second one and find it fierce handy, and I've never once had a problem with it.
Weird. It's handy in size for sure but I am not exaggerating when I say that I was held up at every point in my trip last week becasue of it.
Weird quirk here, you scan the back of the passport card not the front in the e gates. You would think it's the front because of using normal passport but it isn't.
That's odd. I never thought of trying that.
The eGates in Valencia also have a card-sized slot which does nothing.

