I switch between high-intensity full body workouts and muscle group workouts every few weeks, but I almost always do back/bis together. If I do them separately (occasionally I'll dedicate a day to a single muscle group) I tend to not be able to push myself as hard as I'd like, since the other muscle is still recovering but is also involved in the lift.
I try my best not to take health & fitness advice from people working at Starbucks... I hesitate to take coffee advice from people working at Starbucks... plus their "Protien Plate" is shit.