I am 100% confident I have gotten MEN from club members. One was at a meetup earlier in the year. One came from a freebie years ago (different tank I ended up tearing down). It's why I quarantine, I get stuff happens and I don't hold it against anyone. Especially since it was free, and unless proven otherwise I assume it was unknown. I've also once had a tank get disease from a well known online site that sells cleanup crews, and have gotten flukes from a LFS, and .... That class of issues bugs me more, but again, we all kinda know how that is how it goes (that's why I buy quarantined or QT myself all the things, including snails).
I am 100% not going to name names here.
My take, feel free to coordinate with folks who are interested, and as with others go ahead and DBTC with pre-coordinated setups where people know what they're getting. I wouldn't put them in a table with other misc stuff b/c it's too easy to go awry or have someone not fully informed about it grab it.
The practical realities is someone getting a piece, cutting to fresh tissue, and glue'ing to a fresh plug is probably lower risk than someone getting some other frag from the swap (or LFS) and putting it in without doing that. Similarly someone grabbing a sweet, brand new, frag from a LFS to bring in. However, worth making the expectation folks shouldn't bring known questionable things so that new folks don't start bringing unlabeled questionable stuff.