I read one of those click-bait articles on secret iOS 9 features and it mentioned wi-fi assist which switches you to your cellular signal if your wi-fi signal gets weak (less than one bar). It's on by default and the option is located in settings > cellular, then scroll to the very bottom, below the long list of your apps. This seems like a very worthwhile feature. What I found frustrating was that the option does NOT appear when you do a search of the wi-fi options in Settings. The new search feature in settings was intended to help find these obscure options that are buried in a sub-menu, but failed in this instance. Hopefully it will improve. Has anyone noticed if wi-fi assist has actually worked for them?