Whisk together lime juice, lemon juice, grapefruit juice, rice vinegar, olive oil, soy sauce, chili garlic sauce, and honey in a bowl until the honey has dissolved. Season with ginger, garlic salt, pepper, and cinnamon; whisk until blended. Place the flat iron steak into a resealable plastic bag, and pour the marinade overtop. Squeeze out the excess air, seal, and marinate in the refrigerator 1 1/2 hours. Do not marinate much longer than this, as the citrus juice will "cook" the beef.