A solid pair of earbuds should last you at least three years. We are looking for active noise-canceling, or ANC. This is tech that uses microphones to cancel out background noise so you can hear your music at lower, safer volumes. Buying a high-end pair once is cheaper than replacing cheap ones every six months.
Tech brands follow a strict release cycle, usually dropping new models in the fall. This makes last year's flagship model the best value. You get almost all the same features for a much lower price point, especially if you time your purchase right.
The 0% interest period is a hard deadline. If you have any balance left after the 18 months are up, the standard variable APR will apply to whatever you still owe. Pay it off before that window shuts to keep the deal cheap.