You want a handheld gaming PC so you can play your backlog on the couch, on flights, or in bed without being tied to a desk. A good machine should easily last you three to four years of heavy play, so you are buying once instead of replacing it next year.
Hardware refreshes happen fast in this space, but you do not need the absolute newest chip to have a good time. Watch for the major seasonal digital sales when last year's model drops in price, giving you nearly the same performance for a lot less cash.
That intro window is a hard deadline, not free money, so treat it like a countdown. If you still have a remaining balance when the 18 months are up, deferred interest or standard purchase APR will kick in on the original amount and erase all the savings you scored during the sale.