The provider is supposed to do an annual check for the validity of the address you supplied upon application/registration.
If this does not match, your subscription will be aborted.
Also, officially the subscription ends after this year.
After that, you would need to re-register and pay fees for that.
These fees will cost you more than this set top box pack.
This pack also "contains" an automatic prolongation of your subscription.
So if you choose not to take advantage of the set top box pack, you risk loosing this and to pay for continuation of the subscription by re-registring.
Risk, because lately i haven't heared people complaining about this and so i guess C+ simply continues all subscriptions now.
Furthermore, whenever you get into trouble with your subscription, you'll need to call C+.
Such phonecalls will only be accepted by C+ if you call their 09XX pay number, and these numbers cannot be called from abroad.
Lately there is an internet site where you can go to re-activate your subscription card if some activation code was missed.
But be assured the traffic on such a site is monitored and your IP will be logged to see where you are connecting from.
This is a dead giveaway for a subscription that was not meant to be.
All in all you can go for the simplest and cheapest way and be happy ever after, but if you want a bit security built in, you'll need a friend over here.