This effect relies upon a simple gimmick and a standard sleight. The gimmick, is easy to make-and would need to be adapted to other card/box designs. While only one coin travels back and forth between hand and box-it seems possible to have more coins travel-capitalizing on the gaff, the usage of 4 coins, and the premise itself. To do this with 1 travelling coin, as presented, I think to have that coin as a different one-like one copper amongst 3 silvers. That at least justifies the coin's behavoir, and also the presence of the 3 non travelling coins. The gimmick here reminds me of marketed effects-one being the window walket. That prop allows for 3 coins to travel from hand to wallet one at a time. So, I think there are opportunities with this gimmick that go beyond the nice routine presented here. All is made clear and easy in the video. I also can see this effect being connected to a coins across routine, with the card box as the last phase. Nice effective concept worth applying to other coin effects.