Been in Korea for months and I've always seen ade on the menu and I have never tried it before since plain water is basically the only drink I consume.

They serve 500ml & 1litre portions so it's good for sharing definitely! Not sure about the contents but it's prolly soda drink with some grapefruit drink mix (like the Yuzu kind you always see people buy from Korea). But surprisingly I kept going for it although I'm typically not the type who would drink while eating also.