First off they are a tiny bit illegal as they allow you to watch any TV channels without subscribing...
Anyway, basically it connects to the NTL cable network (so obviously you need to have NTL, there are different boxes that work with sky) and to your tv so in that respects its not really like freeview as it doesn't come through your areial, but the NTL socket in your living room. I belive it is possible to connect it up to a PC but its mainly for your telly.
Anymore questions have a look on:
http://forums.afterdawn.com/forum_view.cfm/59
which is a pretty good forum for all things dodgy!!!