The first time the word "neutral" came up here on the Forum in reference to a kite was in a review I did for the Opera IIRC. And RandyG even agreed with me. So that made me feel good. As he is about an order of magnitude better on kites than myself.
And from other people's description of what they think neutral is, the Opera would fall into that category.
I would describe the Mamba more as a bit finicky than neutral. Although in return, it delivers superb return for the correct inputs.
Opera clickable link: