I just don't see an embedded magnet as being the same kind of assistive device as headphones or GPS. Neither of those examples provide a new sense (which was my original comment's example of what an implanted magnet does). They don't replace senses or add completely new ones. Unless someone is capable of storing an entire region's map to memory and locating themselves within that region precisely (maybe some people can to an extent, but not entirely the same).
I'm all for people doing what they want as long as it's not extremely selfish, but I cannot myself see a clear advantage to a magnet implant, other than:
A. Party tricks B. Telling people I have a magnet in my finger
I think it probably comes from a wish for ill-thought out sci-fi tropes with the less than adequate technology at hand.
That's kind of a negative outlook on the whole thing, isn't it? I imagine people said similar things about, for example, headphones, or GPS. And while both of those things have potential downsides, people don't use them because they're too lazy to read a paper map or too selfish to want to share a music experience with friends.