Relief from pain with magnets in my experience has to do with a few things.

1) typically only one side works. I think it is the S pole to the skin.
The other pole may be stimulating and if magnets don't work or make nerves more active just reverse them.

2) I don't know if the attached metal makes a difference. But one has to have magnets that have discrete poles.

3) Placement is a factor. Try putting them on your ankle instead of on the bottoms of the feet. Catching the nerve higher up, is also more effective with Lidoderm patches.

Brian over at PN and I have used magnets for quite a long time.
I use mine for other kinds of pain, knee, back and hip.
Search magnets over at PN to find the posts.
With the big huge ones, I find 20min to an hour adequate, daily.