I bought my iPad Air 2 almost a year after it was released, only a few months before the first iPad Pro was released. I was a little worried at the time that I would get only a couple years out of it before iOS updates rendered it obsolete. I have been pleasantly surprised that that day has not yet arrived—and, based on how the iOS 12 beta is running, that day will not arrive for at least another year.
Last night, I finally installed the iOS 12 beta on it, and found the new OS to be smooth, stable, and fast. All my apps (even the ones I wrote!) are working just fine. As Apple promised, UI and animation-related things like scrolling are visibly faster and smoother, too.
I plan to install iOS 12 beta on my iPhone 7 Plus in early September, after I complete my next release of SwiftoDo. Based what I’m seeing, performance wise, on my even-older iPad Air 2, I’m looking forward to at least one more year of service from my iPhone 7 Plus, too. (It helps that my phone has a brand new battery and a new screen, thanks to AppleCare Plus.)