Wow, I just noticed I haven't used the Whirlwind Shield lately. It sure changed since the last time I played the game... And when I thought I was understanding the discussion, I replayed the game now, and got everything confused, so I'll just discuss my opinion from scratch.
Pressing jump to use the shield's vertical boost is a bit wrong. It's easier to everyone if it's just "Spin to use the shield" instead of "Spin to use the shield, unless you've fallen of a cliff without jumping, or you're tired as Tails."
As I tested now, I found it's really easy to accidentally use the whirlwind after flying with Tails, even when I don't want to. And I think it's just better for Tails to not be able to use the whirlwind at all after initiating flight. Tails can already fly really high, and if the level designer's not careful, Tails can enter a Knux only path using his huge flight ability + a small boost from the shield.