A robot mower handles the one chore nobody wants to do in July, giving you hours of your weekend back. A solid model should last five to seven years if you treat it well, so buying a cheap, off-brand unit usually means buying twice.
Early spring is when new lineups land on shelves, but that also creates a sweet spot. Retailers discount last year's flagship models to clear warehouse space, and the tech rarely changes enough from one season to the next to justify full retail price.
Keep in mind that 0% interest is a strict deadline, not free money. If you still carry a balance when the 18 months end, regular interest kicks in on whatever is left, which quickly eats up your early-season savings.