You want headphones that last a decade, not a trend. Open-back sets give you a wide, natural soundstage, but they come with a high price tag. Buy a set once and take care of them rather than replacing cheap gear every year.
Tech companies release new models on a predictable cycle, usually in the fall or spring. Wait for these drops to find last year's flagship gear at a clearance price. You get the same audio quality for significantly less money.
Remember that the 0% intro window is a deadline, not free money. If you have a balance left when the 18 months are up, you will be charged interest on the remaining amount.