Aside from what the other LN readers have already said, I would like to also add that Myne's method is special because of her being a frail devouring kid who has been teetering on the brink of her own mana killing her ever since she got reincarnated. She basically had to learn to compress her mana as much as possible using her own intuition and imagination, to prevent damage to herself and those around her. Not to mention her mentor and doctor being Ferdinand, probably the guy with the best compression method around aside from her. Meanwhile normal noble kids get to have mana tools and are never in a 'compress/control mana or die' situation nor do most of them undergo devouring (its true nature is not just commoner born with mana), and only learn to do it much later on in their life in the academy as a way to increase their mana.