I know that Apple warns you about the devices that can and cannot take iOS updates. I only wish there was a way to know truly what it would do to your device.
For example, Katie and I updated our iPhone 5Cs to iOS 8.0.2. Mine was fine. Katie's lost the ability to make and receive calls. I rebuilt her phone from scratch and she regained phone service, but lost group iMessaging. Actually, she lost some one-to-one iMessaging as well. We have no way of knowing exactly what she's lost as there is no way to know what was lost. I really need to get her updated to 8.1 but we still won't know what she's lost until she gets hate-phonecalls from people thinking she's ignoring their text messages.
Another example is my iPad 2. I updated to iOS 8.0.2 and it has become so brutally slow. Slow to start up. Slow to log me in. Slow to open apps. Slow to operate apps. Slow to shutdown. As a result, we have not updated Katie's iPad 2 and she's fine with it. Hers works perfectly well.
What I'd love to see from Apple is a way to trial the iOS updates. You can do that with any other computer. If you don't like an OS update, reinstall the previous software. I have friends who disliked the new Mac OS version (dubbed "Mavericks") so much, they reinstalled the previous Mac OS. So why can't we rollback iOS installations?
I realize Apple wants us all on the "latest and greatest," but they have to understand that not all of us can afford the latest and greatest devices on which to run their OS. If that means we can't run all the apps we want, so be it. That's on us.
I really wish I could rollback to iOS 7x.
Although, in the spirit of full disclosure, I did manage to speed up my iPad 2 again by completely uninstalling all social media apps and those that require Facebook login. That helped immensely. But I shouldn't have to do that.