Notwithstanding other's concern this might be too sweet with the addition of sugar syrup, I followed recipe. While not too sweet, it was very cassis forward as would be expected, so if you aren't a big fan of blackcurrants, this one may not be for you.
Cassis is already sweet enough, I do without the sugar syrup (as I usually do). I think the cocktail is best when served in a highball with plenty of ice and a splash of Dry Vermouth.
Was concerned this would be sweet, so we reduced the sugar syrup by half. Was a delightful evening cocktail while watching a ballet from Thearo alla Scalla.