You need a pro-grade external SSD that can handle heavy 4K video editing without choking or dropping frames. Buy the right capacity and read speeds now, and you will only have to buy it once instead of upgrading in a year.
Prices on tech hardware drop steadily throughout the year as manufacturers cycle through new releases. If you wait for the newest model to drop, last year's top-tier drive usually goes on sale for a lot less.
That intro window is a deadline, not free money, and any remaining balance when it ends will trigger standard interest charges.