There's no motivation here to why I, as an iOS developer, would want to use this over UINavigationController. What makes it better? What problem does it solve? The one screenshot it has looks terrible.
I agree the screen shot he used is terrible. Take a look at Path if you have the app. When you tap the Add Friends button in the top right the main view controller slides over to the left, but not all the way. About 20 px remain on the screen. It's a nice effect becaause it gives the user a feeling that they are still "on" the main screen, just tweaking some settings in this underlying part. The transition to settings is less jarring.