After reading through a very wordy blog as part of the UX Design module, the general gist of what I feel that he is saying is that whilst Invisible User Interfaces are appealing, they are a bad concept because they hide all the possible methods of interaction available for both developers and users, they can take away intervention from users in the case of automated controls, and that interaction with the interface does not provide feedback to indicate to a user if their actions were successful or not.
Whilst I believe that a minimalist interface can be useful, there needs to be some kind of feedback to give the user an understanding of functionality. In small devices like card readers this is usually done by LED lights or audible beeps to indicate that the user’s actions had performed correctly or there was an error. If the system is meant to attract the user to continuously use it, then a visually beautiful interface is necessary in order to give feedback to the user’s actions and to give a clear understanding of its functionality. Basically the more simplified and menial the functionality of an interface provides, the less feedback the system needs to provide, but it should give some indication of interaction.