It does seem odd to pay more for less (getting rid of original box) but I guess they rely on you getting used to having the second box then keeping it after the 12 month period so I can see the business reason. I really can't see the point of keeping the box though.
I think I'll give them a call and see what options are available but, at the same time, I don't want to go whinging about cost, pretending that I'm going to leave, when I'm happy with the service - so I won't!
Thanks for your advice everyone - I'll give 'em a call in the morning and see what happens.
Very tempting to get the box though...