How often did something like this happen?
A UI-change is always a challenge for the user, especially for not so tech-savvy ones.
But on the other hand, Apple users have such a high loyality to their brand, that it’s pretty unlikely they’ll loose a relevant amount of users, while it gives a cleaner look to the app, which can be a target for a UI as well and contributes to the general look of the iOS eco system.
You won’t find a UI that’s perfect for everybody, but you can use some maths to calculate if you’ll cause a relevant loss of users when you change the UI.
So in the end, you’ll have to decide what is more important to you: making the the life of some users harder in order to achieve a better look for all or sacrifice a clean UI to make it easier to use for not so tech-savvy users. And for sure, if you develop a single app, you’ll have to consider different things than if you develop a whole OS. And sometimes, it’s just a questions of the designers’ personal favor.
