Well I did the installation and tried the old Sky box with no card and it does work OK on FTA channels and only prompts you for the card on other channels, I even get the full Sky EPG. So you only need the £20 sky card to watch a few FTV channels
In the end I went for a proper Freesat box just to get the EPG and all the channels.
If anyone tries doing it themselves for the first time, I found
this was pretty useful for fitting the connectors.