One of the most annoying things about the iPhone 5 is that it doesn't come with Touch ID, Apple's fingerprint sensor inside the home button. This forces iPhone 5 users to unlock the phone with a passcode every time they want to open the phone.
This might not seem annoying, especially if you've been doing it this way for years, but you'll be singing a different tune after using Touch ID for a few weeks. It's a much faster way to unlock a phone and it's easier on those fingers.
Apple's iPhone 5s and iPhone SE share (first-generation) Touch ID sensors so there's no obvious upgrade there.
Upgrading for Touch ID might seem ridiculous, but once you start using it you'll wonder how you lived without it for so long.