Just because shiny, new iOS 9 is here doesn't mean you should upgrade to it. Here are five reasons not to upgrade...at least for now.
The installer bug still isn't fixed
Plenty of people have reported that their devices lock up when they upgrade --- after iOS 9 has been downloaded, and when they are told to "Slide to Upgrade." It's a total lockup, with no apparent way out.
If that happens to you, you're going to have to try and restore your device to its previous state. It's not a pleasant task. Here are instructions from Apple about how to do it.
When will this bug be fixed? No word from Apple, only that "This will be resolved soon in an upcoming iOS update." So you might want to wait to install until that update comes along.
Your apps may not work with it
Any time a new iOS is released, some existing apps won't work with it. That's been the case with iOS 9. Some apps, for example, have problems with iOS 9's split-screen multitasking. Before upgrading, check whether all of your important apps work properly with it. If not, wait until they are made compatible.
The task switcher is awkward
I'm not a big fan of the new task switcher, which feels much more awkward than the one in iOS 8. I'm not alone; plenty of others have complained about it as well. If you're a fan of the current task switcher, you may not want to upgrade.
Older devices may feel sluggish
Don't count on iOS 9 being a performance enhancer on older devices. It may well make them sluggish. So if you've got an older device, upgrading could slow it down.
Your IT department doesn't support it
In some companies, IT takes a while before deciding to support a newly released operating system because they need to give it a shakedown cruise. If you use your iOS device for work, check with them to see if they'll support it. If not, it's a good idea to wait to upgrade.