This ankle
dorsiflexion machine can definitely help to strengthen the ankle muscles and support the arches, but it is not the most functional ankle exercise.
If I had to choose only one, I would choose balance exercises over
the dorsiflexion machine, but
the dorsiflexion machine can be a great way to compliment balance exercises.
This page has pictures of an ankle
dorsiflexion machine.
Starting Position: Most machines are movable, so position
the dorsiflexion machine in front of a place you can sit down comfortably.