Fedia.io has 422 monthly active users - basically, 422 accounts have logged in within the past 30 days. I suppose I am comparing it to infosec.exchange, which has about 15000 monthly active users. I do believe that fedia.io is the most active mbin or kbin instance, by a factor of 2 or 3, but relatively quiet in comparison to Mastodon and Lemmy.