You reclaim your counter space and ditch the slow pitcher filter immediately. Pure, clean water runs straight from a dedicated tap, and you never have to haul heavy jugs from the supermarket again. Installing one takes about two hours on a Saturday, though you will want to watch for spring home improvement sales when prices drop the lowest.
If you plan on hiring a plumber rather than drilling your own countertop hole, call at least two local trades to get quotes before you buy the hardware. Factoring in roughly $350 for the unit itself, planning your payment properly keeps the upgrade painless.
Keep in mind that the 15-month intro window is a firm deadline, not free money. If you carry any balance past that window, regular interest kicks in on what is left, which quickly undoes the savings from your purchase.