If you're getting an implant already, why not make it an actual smartcard that you can use for WebAuthN, GPG, SSH etc.? :)
On the other hand, the fear of permanently bricking it or messing up the GlobalPlatform card management key has so far prevented me from doing it myself...
Because those cost $350 as opposed to $89, and the install only costs $60, and there is no stopping you from implanting more than one in different locations.
Many people get the small xEM or xM1 first to play with.