Free? What's the catch? I bet it won't be free to BT broadband customers who want it through Sky. They will have to subscribe to BT vision first.
If you are only a Bt Broadband customer, you can only watch it on your tablet or computer, If you want to watch it on your tv you have to pay £5 a month (I assume for the minimal vision package?) and a £49 connection fee.
Cheaper than sky? Yes. Free? Of course not, just a clever marketing scheme.