The question which has parallels and differences at the same time !
The Viewer is the prospect who just reads a free publication without subscribing to it. It means he has several opportunities to use the platform in a free and limited way.
The Subscriber is the reader who has an account and is subscribed to a free or a paid publication. It means that subscriber is in a circle of "relationship" with some publishers and their issues.
Subscriber
5
Viewer