You should not use Magic Eraser on your leather at all as you are wearing away the protective coating over your leather.
Our leather is coated, and a simple experiment can show you this. Water beads on the surface, it does not soak through.
When you use magic eraser on the surface, you are essentially wearing down the "clear coat" for the lack of a better way of putting in of the leather.
The best way to clean your leather is with a pH balanced cleaner and a leather brush.