Which is not that different from paying by the TB, as long as you are big enough that your traffic isn't too spiky. If you assume that over the day/week Cloudflare's your bandwidth usage moves between 0.5x and 1.5x of the monthly average, then paying for 1 TB/month is basically the same as paying for 4.5 megabit/s (1TB/month == 3Mb/s, multiply by 1.5 for peak demand).