I actually am not convinced that this is a good format for intellectual discussion based on past experiences I've had. If you have, say, ten people and are meeting for three hours, that gives 18 minutes of speaking time at most if speaking were divided equally. Of course it won't be and certain people in the group will disproportionately hog the talking time (btw, it is this kind of person who will be most excited about the format). The more nuanced your position, the more difficult it is to express in the short amount of time that you may have to speak. Also consider that some people are simply better at speaking in a group environment even if the quality of their arguments are weak (or at least one sided). One or two people can easily dominate the whole group. It can devolve into a series of lectures rather than a conversation. Or the entire conversation can be sidetracked by something inflammatory that hijacks the group's attention. These issues can be addressed in part with a great moderator, but a poor moderator is a disaster and you may not find out the moderator's weakness until there have already been major problems in the group.

It is no surprise to me that the format is attributed to Jefferson. He seems like he had exactly the personality that would thrive in this tightly controlled environment with rules that he set for his own benefit.

That being said, good intellectual conversation over a meal is one of life's great gifts. I just prefer other formats.