This tends to suffer from the familiar privacy advice snafus. Recommending Signal is problematic if you don't also explain that it requires you to make your phone number public. Not everyone wants to give out their phone number to strangers, jealous ex-lovers, etc. I know there are workarounds with multiple sim cards, but this whole thing is just a bad security model, ratchet or no ratchet.
Recommending PGP/GPG to a tech audience: probably fine.
Recommending PGP/GPG to a non-tech audience: they may just do what Adobe did and post their public and private key, or get them mixed up, then continue believing that subsequent emails are secure. If the user doesn't understand the basics of public key crypto then recommending PGP/GPG without further explanation is probably a bad idea.
@yukiame in bitmessage there is also some attempt to defend the metadata, since the only way of knowing who the intended recipient is is whether the message decodes or not.