In terms of coupon:ammount of charm ratio, boxes for 4k coupons give you 1 charm per 80cp, its by far the best value you can get when you buy charms directly. However during events like lucky board/mission dealer (if you can make use of items you get from board/box), its better to get charm this way, because even though u pay 130 for charm, you get over 50% of that ammount in another power items. If it's only charms you are after, 4k cp boxes are the way to go.