The criteria for selection are political value and propaganda potential. South Korean prisoners of war and citizens who were abducted by the North are picked for their political value. North Korea believes that South Korean demands for the release of all POWs and abductees can be appeased if such people are included. [….]
Once selected, North Koreans go through between one and three months of ideological education at the Unification Bureau. In the early days of the family reunions, the state paid all expenses for the participants, including the clothes they wore. But now they must cover their own expenses. Following the reunions, people can keep their gifts and cash can be deposited in North Korean banks, with family members allowed to withdraw US$100 a month. [Chosun Ilbo]
I’m not sure an experience like this would be worth the pain and the cost, although I doubt that the hostages have the option of politely declining.