In short... Send it back to them or it could cost you.
I wouldn't sell it or bin it if I were you. Under the terms and conditions the box is theirs, you have to give it back to them at the end of your contract or pay for it in full. They were quoting it's value as £299 when they first introduced the box. It would be no good to anyone else other than a standard non-recording freeview box.
If we or you end this agreement for any reason, you must return the box to us. If you fail to return the box we will charge you for the replacement cost, including any reasonable costs connected with getting the box back from you
Don't hold your breath waiting for them to ask for it back though, I would ask them how they intend to collect it. I'm building a steady collection of Orange/EE routers, power supplies, etc. they have only every asked for one of them to be returned. They used to have a freepost address and all you had to do was stick it on your router box and take it to the post office. This was the case with the BrightBox router that came in a postable box, during the Orange days. I don't know about these days.
Like I say don't hold your breath, if they chase their hardware like EE customer services chases return calls then they will have probably forgotten about you already. I'm still waiting after 2 months for a return call about my faulty broadband.
There is also another point in the T&Cs that says...
If we don�t need the set-top box back and you need to dispose of the box or any other equipment, then please give our customer services team a call so we can discuss responsible disposal.
Edited by deleted (Sun 01-Mar-15 20:28:42)