I actually started on Kbin.social, but then it got shut down, Kbin died and now fedia.io seems to be the largest one running MBin. I like the interface on MBin and I guess it’s good to have a diverse fediverse with different services, but at the same time, why use mbin when everyone congregates on lemmy instances? The local magazines on fedia are for the most part, quite dead, when compared to lemmy collections. In the end I feel like there aren’t enough people to go around to support many more services like MBin and Piefed.
A lot of the major federation issues in kbin were already fixed on mbin. Also, there were at least two major federation issues caused by Lemmy updates, which had nothing to do with kbin nor mbin and affected Lemmy instances accordingly as well. Of course, new issues can arise, but that also goes for Lemmy, or even just ActivityPub in general. But overall federation seems to be working fairly well right now.