We have used MRI magnets 1000s of times more powerful then the little magnets they sell for pain or injury, no effects of any kind have has ever been detected. The fact is, you can test the magnetic field with a few pieces of paper and a paper clip. The clip will fall with 2 or 3 pieces of paper between it and the magnet, that shows the magnetic field will not penetrate the skin never mind muscle and bone.
benefits of magnets= placebo effect