If I'd give her the walkie-talkie then my wife would call her every 10 minutes and ask her where is she. Tracking her with a GPS would keep me calm but I don't think it will help my daughter.
The only time I freaked out was when she removed the watch and she didn't come home on time: I went out to look for her and in the meantime, she went home. Realizing that she may go home on another path I went back home and found her watching TV. Honestly I think that those devices are meant to keep the parents calm, not for the sake of the children.