I'm not 100% sure but I think this site would not be allowed in Germany because of consumer protection laws. In that regard it's very telling that justfab.de has a very different checkout:
I think the law in Germany even states what kind of text is appropriate on the "buy now" button.
Maybe the fee is mentioned on a other screen.
As far as i renember it is not really "illegal",but the contract is invalid.
You're then stuck arguing with your card issuer. In the UK for example, you're shit out of luck unless the transaction is > £100 where the card company becomes 'jointly and severally liable' which allows you to pursue them instead.
Obviously this varies so it all depends on where you are and where your card was issued as to how much chance you have of 'refusing to pay'.