I put that in there because I'm just one person, working on this in my spare time. I don't think there are any immediate vulnerabilities in KBSecret itself - that's more of a warning that I'll probably be breaking things as I work towards a stable release.
As for KBFS, I can only relay my experience. So far, it's been completely reliable for me - no crashes, hangups, or lost data on what I assume is a lower-priority target for them (Linux).