Hello, Badmus. To answer your questions:
You will have to renew your subscription once it is exhausted. We are not a service provider (only a device manufacturer), so you will use your 10GB from the provider on the BRCK. Once this is finished, you will have to renew it.
You cannot stay on the internet for free with the BRCK, or with any other device, since someone has to pay for the cost of connection and that someone is often the subscriber.
We offer a six-month manufacturer's warranty - if your BRCK is not working straight from the factory, we will offer you a replacement within six months (provided you don't open it up and thus void the warranty).
Does this clear things up?