It lacks reasonable audit capability. Paper ballots can be inspected and recounted; tampering and ballot stuffing can be observed. Tokens in a particular bin

It lacks reasonable audit capability. Paper ballots can be inspected and recounted; tampering and ballot stuffing can be observed. Tokens in a particular bin can't be audited in the same way. And it may also lack anonymity--unlike the folded paper vote, you could be observed putting the token into a particular slot.