Why "yikes"? I don't think that's common anywhere, but the intersection between "hardware hackers who uses Flipper Zero" and "people with subdermal implants" is probably bigger than the intersection of "people not being hardware hackers" and "people with subdermal implants"

It's not common in any country, it's a fringe biohacker kind of thing.

There's a small group in the US that does this kind of thing: https://en.wikipedia.org/wiki/Grindhouse_Wetware

It's not exactly common in the US, but enough people have them that it isn't surprising to see.

Perhaps we run in very different circles, but I would be pretty surprised to see them!

“Move along, clank” indeed.