I'm happy for this, but I'm not excited. Been jailbreaking for a long time, and people with themes have created much better visual options for iOS for a long time now. And no, not all of them lag or slow down your device, especially with the newer ones.
****, people have created some really beautiful themes for the Messages app, and right now on stock we're stuck with a really unattractive grey with either bright green or blue. iOS is essentially bereft of customization other than for how you'd like to receive notifications.
What I'm getting at is: iOS feels really, really bland, and there's just about nothing that makes you feel like the device is "yours." And unfortunately, Apple doesn't really care much for adding customization options into the Settings. Things that are resolved by things like biteSMS (no longer updated, but other tweaks fulfill some functions,) Activator, Winterboard, Messages Customiser, TinyBar (****ing love this one.) That's just to name some, and these have been around for a while, but we fail to get anything like them unless you're lucky to be on an OS version that has a jailbreak available.
And again, to those that scoff at it, no these don't lead to a "slower and choppy OS experience" or an "unsafe device."