You are buying a proper mechanical keyboard and mouse set to fix hand strain and make typing all day feel like less of a chore. A good setup built with hot-swappable switches and solid aluminum frames should last you a decade if you clean it once in a while, meaning you buy it once instead of replacing cheap plastic gear every two years.
Watch the release cycles closely because companies drop updated versions every fall. When the new models hit in October and November, last year's top-tier boards usually drop in price even if their performance is practically identical.
Just remember that the 0% intro APR for 15 months on purchases and balance transfers is a hard deadline, not free money. If you still have a balance left when those 15 months run out, interest will get charged on the original amount from day one.