> The umbrage that the GP seems to be taking is that Signal doesn't require you to verify your key, nor is it particularly visible.

Only the latter really, but yes. It doesn't need to be required -- see the footnote text where I elaborate: Threema also doesn't require it, but it's very visible, so people do it and thereby avoid having to trust the server.

> only really starts bugging you about verifying keys if they suddenly change

Does it? I haven't seen that, though I think the only key changes so far have been in group chats, perhaps that's different. This would be quite an improvement over WhatsApp that I wasn't aware of (if it really does this).