“I already use and/or iPhone UI Kit / iOS 9 GUI document for Sketch. Why download another one?”
Put simply, this one is better.
More complete, more up-to-date, more accurate, and more thoughtfully structured iPhone UI Kit for Illustrator and Sketch. If you use Illustrator, there’s no contest — you won’t find another iPhone UI Kit resource remotely close to this breadth or quality. Even if you have another good iPhone UI Kit doc for Sketch or use the one that comes bundled with the application, you are going to want this one. It’s a better kit that will make it easier and quicker for you to create the best iOS mockups.
This iPhone UI Kit is based on the upcoming release, and includes new additions like Night Shift as well as recent changes Apple has made to system apps like Music and News. You can rest assured that the screens you are referencing here are as up-to-date as any kit you are likely to find for iOS 9.
Great effort was taken to ensure that each item, object, and icon was accurately recreated. This means that even though each item was redrawn to be fully vector and scalable, each object was meticulously compared to the source screens in Illustrator’s Pixel Preview mode to match the originals and should be virtually pixel-perfect at 2x resolution.