Praise be to Allah.
There is nothing wrong with using a credit card which the customer has loaded with the amount of money he wants, and there is nothing wrong with the issuer charging commission or fees in return for offering this service.
There is nothing wrong with buying items with this card over the Internet, except in cases where it is stipulated that there should be a hand-to-hand transaction, such as gold and silver, because it is not possible to do a hand-to-hand transaction in that case.
See the answer to question number 89787.
From looking at the site mentioned, it is clear that dollar exchange rate on this site is higher than the market rate. There is nothing wrong with that, because those who are engaged in money exchange may agree on whatever price they want, but it is essential that a hand-to-hand transaction take place immediately in a true sense. If the one who buys the card pays riyals and immediately receives a card that is loaded with the equivalent amount in dollars, then the required hand-to-hand transaction has been achieved.
When buying these cards, one should beware of dealing with untrustworthy parties. We do not know anything about this site or the people in charge of it.
And Allah knows best.