You do need a card for the 30% coupons, but their card has no annual fee and as long as you pay the bill in full when you get the statement, you don't pay interest.
Often if I don't get the 30% mailed to me, I'll just find the code online and shop at their website, as long as I spend $75, it's free shipping! I shop at Kohl's mostly for more expensive kitchen electronics (Cuisinart food processor, Kitchenaid mixer, Caphlon cookware, etc.) so I'd rather have them ship that heavy stuff to me anyway, beats lugging from the store to the car and then from the car into the house!