This saddle will allow you and your horse (or other mount), to fly at high speed. It does not however, prepare the animal for this in any way, causing it to panic and requiring that you keep it calm and try to stay steady while flying.
In a roleplaying game, you could fly at a higher speed than your animal runs, but require handle animal or similar skill checks in order to remain on the animal. Maybe it could even grow accustomed to it over time, and require less difficult checks, or develop a desperate fear of heights and get even harder to stay on each time you lift off. Story-wise, it would be hilarious and terrifying, and probably create some tension depending on how everyone feels about the animal.