Driving a car through the dark, wet roads of late autumn is miserable when your stock headlights barely cut through the fog. Upgrading to a high-output LED setup gives you the visibility you actually need, but quality kits aren't cheap. Running a car is a steady stream of tires, oil, and insurance, so dropping three hundred bucks on bulbs all at once stings.
Autumn is the right time to buy this gear before the shortest days of the year set in, and prices stay fairly steady right now. We aren't talking about a new vehicle here, so you don't need to negotiate the price of a bulb kit like a used sedan. You just want to find the right part number, time your purchase, and manage the cash flow sensibly.
Keep in mind that the intro window is a deadline, not free money. If you still have a remaining balance when those 18 months are up, standard interest charges will apply to what is left.