YouTuber iAppleBytes has done a speed test video comparing iOS 10.2.1 beta 4 and iOS 10.2 on the iPhone 6s, iPhone 6, iPhone 5s, and iPhone 5. He compared the boot times of devices along with their app opening times. While the iPhone 5s does boot a bit slower while running iOS 10.2.1 beta, there is no noticeable increase in boot times in any of the other iOS devices. When compared to iOS 10.1.1 though, some iOS devices like the iPhone 6s and iPhone 6 do report an improvement in boot times.