Other reviews

These reviews of U2F "Secure Keys" by Adam Langley and Brad Hill are interesting if you like the idea of something you can put in your pocket but do not, it turns out, have much call for PGP or SSH keys. Some of the devices they've reviewed can do SSH or PGP too, but all implement U2F which seems to be the current "great hope" for a vendor neutral physical second factor (a big step up from sending messages to your mobile phone).

https://www.imperialviolet.org/2017/10/08/securitykeytest...
https://github.com/hillbrad/U2FReviews#u2freviews