Jim VH (a member in this forum) made marmalade out of ripe orange kabosu fruit, which I was able to taste. I think this fruit has a lot of potential for marmalade, since when ripe the rind is semi-edible, or at least not too bitter. However, traditionally in Japan kabosu is picked while still green before it has turned orange (actually a slightly yellowish green color) and is used more like a lime or lemon. Picked orange, it's a little bland and not the most flavorful, but the peel works well in marmalade and is softer than the rind of orange. It does have some pleasant aromatic fragrance, almost half like Yuzu I would say.