Cortana comes to the Apple iPad with an optimized UI that fits the larger screen sizes
In addition, the changelist for the app points out that Cortana now opens 20% faster. That means you won't have to wait long to have your inquiry answered, or task taken care of. Even though Apple allows third-party assistants to work only through their apps, Cortana will still be able to track your packages, set reminders, give you the weather, news, sports scores and stock prices. On Android, Cortana's capabilities are greatly expanded since it does have access to the operating system.
If you're feeling a bit let down by Siri, or just want to see what Cortana is capable of, you can install the app on your iOS device by clicking on the appropriate link. We've included the Android version of Cortana for those who would like to see what she can do on Google's open source OS: (iOS|Android).