Microsoft has updated Cortana for iOS adding support for the iPad. The new version has a layout designed for the larger iPad screens and according to the release notes launches 20% faster. Unfortunately Cortana on iOS doesn’t have access to the system in the same way as it does on Android.
It has widgets you can add to you the lock screen and the today view.
If only Cortana could talk to my smart home, then it would get a bit more use.