IUP is a bit more expensive but more convenient, depends what you value more.
Not really more expensive. There's always a gamble when selling your phone after 11 months. Sometimes you get more than what would be left over at 12 months on the iUP and sometimes less, especially once you factor in time, effort and any cost of dispatching it. You're not paying the full AppleCare price if you upgrade after 11 months. There's no interest on the money you're paying.