Is it effectively a competitor to Lemmy or Mastodon at it's heart?

I think it is, to an extent, but seems more flexible in its range of potential uses. So Bonfire social definitely is, but the Bonfire Science, and Bonfire Communities add a bit more flexibility in ways to structure the communities and groups within those communities. I like the ideas driving it, one of the problems i find with Lemmy, is the inability to organise on platform beyond a reasonably casual exchange. It makes things slow, and hard to communicate through.

The boundaries thing is cool, i'd forgotten that was part of it, the circles i think makes more sense when you look at the different use cases like the science, or community projects. But yeah its just a grouping mechanism.

~topic based

This is the best use for social media. I can't see the use case for non-public figures on a platform like say twitter.

~scale

Yeah, its a good question. The more complicated a structure, how well can something like a bonfire communities scale before groups become meaningless. Maybe its a better as literal town size, but hard to see tens of thousands in circles being an effective use case. I've watched this project for a few years now, and i've not seen much in the way of growth, so i'm not sure they would've come across the challenge yet.

I suppose for security in scaling the boundaries function could really come into its own, it seems more fine tuned than the heirarchy of admin/mod/user.