That being said while iOS 9 held a lot of promises and introduced a host of changes, it also came with a fair share of problems. For example one of the issues some users have been complaining about is battery life, which is ironic given that iOS 9 comes with features meant to help conserve battery.
There is also the issue with notifications in which several users reported that their notifications are not coming in properly, meaning that they will not sound so users might actually miss out on messages and emails unless they have their phone in front of them. Now Apple has been working on bug fixes with the latest update being iOS 9.1 that was released yesterday.
It fixes some bugs but not all of them, but hopefully the annoying ones have been addressed. iOS users who have yet to update their devices should probably go ahead and do so.