Don’t those run afoul of the linked white paper (under “dangerous” in the 2nd paragraph), which talks about the attack paths made available if an RSA key is used for signing and encryption?
Those tools are not meant for sender authentication. If you want that you would have to first share the senders pubkey with the recipient, and sign your message with the corresponding privkey.
As I commented in https://news.ycombinator.com/item?id=19953623, I’d love to see another blog post walking folks through why/how the “dangerous” RSA keys are in fact useable for both operations because the textbook RSA concerns aren’t a concern because of X, Y, and Z.