It's fine. I've garnered over $5K in Amazon gift cards (all electronic) in the past 5 years through various sources like sites where you earn gift cards. It's a long ass code and you put it on your Amazon gift card account. You cannot transfer the code once it's used, nor can you transfer part or any of your gift card balance once it's been redeemed in your account.

When you buy something, it'll use your g/c balance first, then your default payment method next to make up any difference.

Amazon is a big, long-term, reputable company. There's no reason to think their gift cards are fucked up.

Yup. I absolutely love them and always have my friends and loved ones defer to them as the gift of choice for me. My family in the States is even able to use the Amazon Germany webiste in English and top up my German gift card balance and it works beautifully. Hope that helps and "Happy Shopping"