So the term “instant approval credit card” is not a good way to distinguish one type of card against another.
The only thing that matters is the condition of your credit history as there are options for those with bad, fair and excellent credit.
What makes them “instant” is that you typically apply online, the carrier does a preliminary check on your credit score and then reaches a decision within a few minutes.
When applying for instant approval credit cards for bad credit (those with credit scores below the 580 range), card issuers could either provide a secured or unsecured credit card appropriate for those in this category.
Obtaining this card gives you the ability to make a deposit, say $200, which would be used to pay off any purchases in case you got behind on payments.
With these no deposit would be necessary, however, because you'd be a risk to the carrier by having poor or no credit, you'd have higher interest rates and perhaps a fee as a condition to use the card.