It has been close to three years since having a magnetic disc installed in the tip of my right ring finger. It still appears to be perfectly intact, and has given me no trouble at all so far. It has become seamlessly incorporated it into my sensory perception, much like taste or smell. I don't think about using it anymore, I just use it.
Recently at a self-checkout kiosk I scanned an item, and felt a short burst of electromagnetic pulses. The kiosk was destroying the hidden anti-theft tag on the item. There was no audible or visual indication that this had happened, but I had felt it happen. It wasn't just a sensation of vibration. I felt the event in vivid detail, like hearing a silent sound.
I truly hope that a commercially viable magnetic sensory implant is produced. When I hear about "grinders" coating magnets in hot-glue for implantation I cringe. While the parylene coated stir disc has served me well, I can only dream of a home implantation kit consisting of a syringe loaded with a purpose-made, biocompatible implant. Until then you'll just have to take my word for it: having a magnetic 6th sense is awesome.