The split seam.
The thing I never liked about the front pocket style wallet was that they can be a pain to use.
As you put cards into the exterior card slots the sides of the wallet press outward from the card. Which means that when the outside is full of cards it’s a pain to get anything out of the big center pocket.
I fixed this by splitting the seam down one side of the wallet. This lets the wallet expand as you fill it up, but you can still access the center pocket.
The opposite side is a full seam. So that end still pinches the contents of the center pocket so nothing falls out.