If Mbin is meant to be a "Lemmy and Mastodon client" alone, then it is a quirky Lemmy "app" and less responsive Mastodon "app".
But it shines only when it scales. This, however needs more users taking use of eg. magazines' custom CSS (and these don't even federate!), keeping track on most popular Mastodon & co hashtags, adding these tags to Mbin magazines, following outside accounts to federate them to instance, etc...
All the Great Exodus fledditors, people craving for non-tankie Threadiverse service, and also curious fedinauts from outside made this happen on kbin.social, and this is what I loved in it the most.
Mbin happened when kbin.social was already crumbling, but many of its users (me included) still hoped for it. When kbin.social definitely collapsed, the previous kbinauts were already aware of not-tankie Lemmy instances, like sh.itjust.works (hosting MeanwhileOnGrad), sopuli.xyz, or generic lemmy.world.
Maybe the more aggresive Mbin marketing (have you seen the sidebar of this community - it still mentions "KBin"...) would help Mbin - but only at cost of making drama with existing kbinauts. With Lemmy's toxicity problem being talked much recently (and instances being closed because of it) I am glad, that things did not go that way.