Like anything, it would depend on a number of factors, including where you implant. Knife edge is always risky… more risky for someone who uses tools or does physical labour or, sports, as opposed to someone who hardly goes outside.
I think the issue is more likely to be the expiry date of the card.
I think you are completely right in what you say. It has a lot to do with the job you have, whether you do extreme sports, whether you ride mountain bike and what was mentioned above, but where else could it be implemented?
Is it possible to implant these “certain payment device” (from My Custom Payment Conversion Experience) conversions to the “forearm extension” of the knife edge?