And what about online tutorials, marketing, user manuals, customer support? You probably want your app to look consistent with that too, right? Do you really expect or even want to sift through multiple different versions of tutorials and guides?

As long as an app is easy to use, people prefer a single look. No one cares about "looking like the OS", except maybe 0.1% of users.

Until you want to explain to your friend or elderly parent with a different phone how to use the app.

And devs would rather the opposite.

Subzero