I have had a small explore with a data explorer query and a poke around and it does look like @mentions are going out even though the category is default muted, which is a bit of a spanner in the works.
I’m reasonably sure that shouldn’t happen, but people have also said that even the proper ones (ie. getting a notification for being @mentioned in a summary they’re not expecting to be muted) are also too noisy, so we may have to forgo the @.