These apps have chosen to reduce details to achieve a minimal UI,
but in the process the UI has also become harder to use.
Unfortunately a UI walkthrough is quite an inelegant way to
explain the core functionality of an app. It can be a frustrating
obstacle before you can dive into an app, and you have to remember
all of those new ways of using it once you get in.
A good rule of thumb is that the user should be able to figure out how to use an app just by looking at it.