We ordered it, waited for it, cancelled sky (who offered us a discount if we stayed). Eventually the man arrived to install it, it wouldn't work - why? our broadband speed isn't fast enough here. You'd have thought bt would know that. We then had to restart sky.
BT vision is just freeview, and a freeview recorder box. We have it and it is great. Cost us about £100 one off fee but may have changed. Think you have to have their broadband and possibly phone line. We think it is great. We had a few problems when we moved and their customer service/support were rubbish. But other than that is is great.
You also need a working aerial capable of receiving a digital picture. We were not told this and when we got a quote for repair to our aerial etc it was almost £250. Dh phoned Sky and cancelled the cancel.