We are using it for essentially all of our prototype boards here at Oxide (low complexity, low layer count) -- and keeping a very close eye on it for our larger boards, where we still suffer from proprietary software. (And to be clear, when I say "suffer", I don't mean the mere principle but the true pathologies of proprietary software: license servers dying; licenses expiring incorrectly; software dying, costing lost work; formats being proprietary; etc. etc., all of which we saw over the course of building our boards.) We've been waiting for KiCAD 6 for a while, and while it's not yet to the point that we can use it for everything, it's definitely on the right trajectory!