iOS 9 brought more speed to some earlier devices and slower interface on newer devices. I have read alot of posts and tried iOS 9 my self, its good and a bit bad in the same time. iOS 9 issues can be divided to : 1. Battery life problems 2. App Switcher bug and Frame dropping (especially on newer iPads) 3. Bugs and lags that come with every new update. Discussing these issues : Issue #1 : Battery life, every one using iOS 9 is experiencing Battery life issues especially on iPhones as they already have a small battery, if u believe iOS 9.1 beta is fixing those battery life issues. The answer is NO, its even making it worse, the battery life issue will not be only on iPhone but will affect iPad as soon as the update is released, i have noticed battery issues on my iPad since iOS 9.1 Beta 1 (Maybe next betas will improve the battery life, Issues iam talking about are just the ones in the present, so i dont know if iOS 9.1 beta 4 or 5 is going to fix any thing soon. ). If u are on iPhone 4S and later and u care about having enough battery for the rest of the day, stay on iOS 8 if u didnt upgrade to 9 until apple releases the fix. If you are on iPad 2, mini 1 battery life and performance are ok. iPad 3 and later, stick to iOS 9.0.2 if u upgraded. Issue #2 : App switcher bug and frame dropping. This is a major issue where iPad 4, mini 2, Air lag with a very bad animation in the app switcher when scrolling or choosing a certain app (it doesnt affect the iPad Air much like it affects the mini 2 and 4). Frame dropping can be mostly noticed when quitting a graphic intensive game or some times in apps where there is transparency or translucency. (Affects most iPads starting 3 and later). Issue #3 : Bugs that come with every major update. We have all tried alot of iOS versions. Personally, i have tried iOS 6 and later. iOS 6 didnt have much issues (all devices were very close in terms of performance). iOS 7 introduced a new graphical intensive interface which actually uses most of the RAM while doing a simple task in the homescreen, iOS 8 probably made it a bit worse on some devices and iOS 9 seemed to fix 90 % of what iOS 8 ruined but in the same time introduced a set of bugs that annoy many users. I hope Apple is going to fix some bugs with iOS 9.1 and 9.2 so that every one would have at least an OK experience with iOS 9. In my opinion, i think iOS updates would be better on a 2 year scale just to give apple more time before releasing a new major update to make sure its atleast 90 % bug - free. The 1 year scale is a bit unstable as every year apple releases a new update that fixes the older updates bugs and in the same time introduce a whole new set of bugs that need time to be fixed and the cycle goes on with every iOS update.