As demonstrated here this person has a very low muscle tone in some areas. An ankle foot orthoses or AFO is being used because this person cannot activate or move the ankle joint through normal range of motion (commonly called ‘dropfoot’).
In the photo that’s the opaque plastic device running down behind the calf and into the shoe. It mechanically holds the foot at 90 degree in sagittal plane (or side-on)
However in this case the person also has weak lateral (outer) stabiliser muscle groups or perhaps unequal lateral/medial ankle muscle groups.
The Float or Flair can clearly be seen to help stabilise and for such a small and lightweight modification provides a surprising amount of alignment improvement.