Sky Freesat Card question...?

I am currently using my old Sky box to view just free-to-air channels - BB1, 2, ITV, ITV +1, C4, E4 etc... I am not a Sky customer anymore, so don't pay anything, just use the old box and satellite dish to view these free channels. I have been told that for �20 you can buy a Sky Freesat card that will give more channels than freeview does.... Is this correct? What extra channels does it give?