A good e-reader with warm light and physical page-turn buttons is a buy-it-for-life device, or at least a buy-it-for-five-years one. You want to buy once, get the hardware that stops eye strain, and ignore the yearly refresh cycle.
New e-reader hardware usually lands in late fall or spring, which makes mid-summer electronics sitewide sales the sweet spot. That is when retailers discount current models to clear inventory, and last year's flagship becomes a much better deal than the newest base model.
A 0% APR period is a strict deadline, not free money. If you still have a balance when the 15 months end, regular interest kicks in on whatever is left, so set your monthly payments to clear the full $250 well before time runs out.