We did a rim of Davidson Plum powder and sugar on grapefruit juice (extra zesty and the colour complements the drink) and reduced the grenadine to 5ml while upping our own passionfruit syrup to 10ml. Not at all too sweet as other commenters found it. Delicious.
Liked this, but did find it a bit sweet. May be more of a 6 than 7 on the sweetness; however, it could be my pink grapefruit as we live where grapefruit are picked ripe from the tree and a bit sweeter. Did put some ice in the glass. May benefit from a splash of water before shaking. Enjoyed it.