Why a cover for the overlay?
Irlen Overlays are great.
They reduce distortions and visual stress due to reading
Sometimes they allow for enormous improvements in reading
But for most individuals, they should only be temporary
Overlays do not help in dealing with bright whiteboards
They don't help if visual stress results from writing on white paper.
Those who have light sensitivity due to bright lights or sunlight are not helped.
GIving out appropriate information about overlays and Irlen FIlters will help people understand the differences, and what they need.