Very enjoyable, easy to drink. After reading the comments, I tried it two times, both without sugar syrup, and increasing to 1/2 oz the grenadine syrup. I found it better with only light rum (the first time I put a little bit of Smith and Cross). I still found it quite sweet, maybe I would try next time with the right amount of grenadine and sugar syrup (and another time without sugar sirup? And maybe another time...).
Tried with spanish pomelo instead of grapefruit... I think it wasn't such a good idea. Next time I'll try it with proper grapefruit !
Probably not my favourite mezcal cocktail anyway.