not sure what your point is. cash back cards aren't really interesting to me. you're better off not overspending on things that don't add to your quality of life than worrying about whether you're getting 1-3% cash back.
i do have a premium travel card that gives me points for dining and travel but these come with high annual fees so you're paying for it in a different way.
The point is that most people don't bother to juggle cards to get the best cash back each time; they just pick one and stick with it (which is why companies PAY Costco big bucks to be their card provider).
If it’s at 0% why not (genuine question). That’s just free money, right? Obviously the interest on $300 isn’t much but if you take 0% loans on everything where it’s available it will add up eventually.
i used to be really into optimizing cash back but it just ends up costing more mindshare than it is really worth.