Well, if you, for example, buys a 200 voucher, and this will then be sent with a uninsured letter from Amazon, there are doubts about the honesty of his fellow men (a la 'What happens if the voucher is intercepted on the way?'). Quite absurd this is certainly not because the letters do not come incognito, and the plastic card is possibly palpable.
I have chosen to print - to be on the safe side! The individual picture / photo then also make very nice.
Alternatively, one can use only the number of the voucher, and use a separate gift card / greeting card. You just have to make sure the code / number of the expression 1: 1 pass on to the recipient.
And there's nothing faster than self-expression :-)