I didn't know about these, but I think they look great. I am not against locking down hardware if that hardware has a very specific and tailor-made purpose for security, and this seems like a really good and fairly cheap solution. I wish my government offered them as an alternative.

You could also imagine having them integrated directly into the phone, but with a physically separated button or fingerprint reader to authenticate. The TAN generator could even have the ability to override the display to replicate the UX of authenticator apps.