Andrew Cunningham for Ars Technica:
For the first time in a while, I’m comfortable recommending the latest version of iOS for the oldest-supported iPhone without major caveats or qualifications. Yes, newer iPhones are faster and can do more things, but if you’re still using an iPhone 5 or 5C (or if you’ve handed your old one down to someone else in your circle of family and friends), iOS 10 will treat the hardware about the same as iOS 9 did—not bad, given that the iPhone 5 is four years old.
I wasn’t using an iPhone 5C as my daily driver, but I did load the betas on it and have been very impressed with the performance. You shouldn’t hesitate to install this update if you have any supported device it runs on.