My wife and I each have an iPhone 5. We don't use the phones much and for that reason don't really want to spend a lot of money for replacements. We use our iPads or computers for most things. A few questions: (1) I know the iPhone 5 is stuck at iOS 10, but if we don't care about the newer features available on the phones, is there a reason (e.g., security) that we really should upgrade? (2) If we do upgrade I was thinking about getting a refurbished SE and/or an iPhone 7. How long would these likely be able to be used before having to be replaced. (3) What iPhone is the best value in terms of price and expected longevity at this point (again, assuming the latest bells and whistles aren't desired). Thanks.