There are readers the size of a thumb drive, cards themselves are the standard credit card size or even SIM card size if not contactless. It's not the real issu

There are readers the size of a thumb drive, cards themselves are the standard credit card size or even SIM card size if not contactless. It's not the real issue here, there are a few more important ones such as lack of desktop browser support for U2F NFC use case. U2F applet works fine for me on Android though.