Using a Credit Card and Getting Cash Back in the Form of a Check?

So my aunt has a credit card where if they spend money using it they get money back, having kets say they spend $100 and when they get that payment notice in, and pay it off, they get money back from using said CC. But are those types of credit cards worth it? Because I think it's cool you're earning money for spending money but you still have to pay off that balance by the end of the month and what if you spend 1K and then you can't pay that 1K in full, and you get charged interest and it ends up being 2K you gotta pay back instead? I've never had a credit card before so unsure on how they work.