The Samsung Secure Folder was first launched along with Galaxy Note 7 and there it was given way to some more Galaxy A-series models. This feature is based on Samsung's "defence-grade" Knox security platform which is designed especially to create a private, encrypted space for its users where they can store their images, documents and apps. Samsung declared during its release that ' users can benefit from this feature by storing and encrypting their personal and private content.'
They have specifically told about this app that it would be compatible only with the Samsung Galaxy smartphones or later versions which are running Android 7.0 Nougat and the app has to be be downloaded only from Galaxy Apps store.
So it is clearly for those who are using this model, and unless the app picks up the craze, it is going to be used only by Samsung Galaxy users.
As I am not the one who could use it currently, I am unable to give you a first hand user feedback.