You want a fitness tracking smartwatch that actually lasts, tracks your sleep without dying by afternoon, and doesn't get sluggish in a year. When you spend around $450 on tech like this, you want to buy it once and keep it on your wrist for the next five years, not upgrade again next fall.
The secret is waiting for the newest generation to drop. Prices on the current model usually dip right after the new one hits the shelves, or you get the fresh features if that matters more to you. Either way, timing your buy saves you from paying peak price for tech that is about to be replaced.
That 0% window is a hard deadline, not free money, and any leftover balance when the 18 months run out will get hit with standard interest.