One thing, I kinda thought the prototype would be more... patchwork materials. IIRC, the novel also described it as such with whatever they could gather in town - and with people doubting the prince here. But it has been a while so I could be wrong. Still I think the artist drew it too much like a modern balloon.
But that's a minor gripe.
One other thing I think I recalled that's missing (but it could be next chapter)