Looking at the comments, I modified it to 60 Vodka, 50 Pink Grapefruit, 20 Cassis. It was a refreshing bitter sweet cocktail. A nice balance of the ‘tang’ of the grapefruit with the fruity cassis.
It's fine, but not sure I'd go out of my way to make one. If I've squeezed a fresh grapefruit, I probably want a drink that keeps things very grapefruit-forward, whereas here the cassis just detracts from it a bit I think.