This is just great! I found it rather rich, but man is it moreish... I used 100% pure cranberry juice (which I keep on hand for my cosmopolitans, too - I like to adjust the sugar myself) and found that a mere 2.5 ml of sugar syrup was enough for a perfectly balanced cocktail. This is definitely going in my permanent rotation!
I can confirm that using Earl-Grey-infused syrup rather than gin also makes for a delicious cocktail. I feel there is also less risk of over-infusion - or at the very least, it's less of a waste if you just ruin a bit of syrup, and not 2 ounces of good gin.