@gaelle Yeah, thank you. Incidentally I switched to this Setting last week after writing a new blog post. I didn't know about it initially and it turns out that many other users don't know this either. In the meantime I accumulated over 1000 spam comments in a very short time by the way.
The only thing I can say is it works – spammers don't have Vivaldi accounts. I also thought about setting the word blacklist, but didn't test this as the registration setting is enough.
And an additional comment about the automatic spam check: Turns out the check only works, if you enable it by having a paid Akismet account. Probably not worth it for a casual blog.