If you have one of these be sure you check out the airfares. Since a lot of them require expensive seats it can be cheaper to buy two tickets. Plus both parties must have the exact same flights. (I had a friend who traveled with her husband on one of these, he had to return home early and she wound up buying a full fare ticket since she did not go with him!)
Full fare tickets are often just sky high. A full fare ticket for me from Nashville to Atlanta runs $1000!!!!