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.
I agree that the more subtle approach is usually the best for slightly hidden or ou of place features but when you try to push the boundaries of touch based interactions and not include some tutorial or walkthrough, you run the risk of fatally slow discovery of features. Max also states that when you move to a minimal UI you reduce details, to which I disagree.
You can certainly achieve a minimal UI without reducing details. have a look at Check The Weather app on iOS which does an amazing job of packing in nothing but details combined with a minimal UI. They are a gesture based system which has a UI walkthrough hidden in the help menu.
When it comes to teaching users to use your UIs, I would recommend to do so mainly by progressive disclosure with slight visual cues and subtle animations - only use a walkthrough as a final resort.
If you app is complex and deep or an entirely new “system”, taking the suggested approach would result in constantly bombarding the user with moving elements which hint at hidden features. Imagine if Check the Weather Had all of its hidden features pop up and down to ‘remind you’ they are there.
In Max’s own app example, he uses the subtle visual cue approach to basically tell the user “Hey, The Ingredient List which is usually the first thing you see on a recipe card is actually hidden on this piece of paper which we are making you swipe over to find” This works well because the user is probably looking for the ingredient list to begin with and seeing the paper slide in is a good visual cue. That whole interaction seems unnecessary to me but the visual cue works fine.
In summary, I agree that when you are providing access to features or options, using slight visual cues are a good idea, but would be ridiculous in practice when all of your “gesture based” app’s features are hidden and you are attempting to achieve a minimal UI. I think that a better approach for these more deep and more complex systems which attempt a minimal UI would be a UI walkthrough within the help system.