This is a rambunctious cocktail at first sip but does mellow with ice-melt in the glass (although ice in the glass is contrary to the instructions). I added 5ml of freshly squeezed pomegranate juice, which did have a gently taming effect. All said, it's a wonderful cocktail!
I agree that this is a fabulous way to showcase Byrrh. With pomegranate syrup (and 2.5ml sugar syrup) rather than grenadine it was an even more complex flavour. And just seemed right!
Best to stir rather than shake. Or, put all ingredients and ice into shaker and seal, but rather than shake, turn the shake in a rolling motion upending each end in turn.