I think the necklace might be better because there are more beads that touch the skin, so more oils would be absorbed. I think...

We have a necklace, that we use as a necklace during the day, and we wap it around her ankle at night.

I also found she needs to wear it for at least 24 hours for it to have an effect. It seems like it has a cumulative effect maybe? I don't know but she wears it 24/7, as I took it off her one day and night, and 24 hours after I took it off her she had the worst night ever.