No, you'll pay nothing until you subscribe. Subscribing is done inside the app, much like an in-app purchase. All options for subscribing are in the app, including the options to cancel your subscription.
The content was starting to get better when the free trial ran out, so I went ahead and got a weekly subscription and then put a reminder in my calendar 30 days down the road. I'll make up my mind more permanently then, based on whether I actually read it regularly.