I'm going to shamelessly borrow your phrasing, because what you've described is exactly what happens: It's a rotation through other participants so neither the study leader nor other individuals have to "[carry] the conversation." It's really interesting, because it fosters conversation that can lead to interesting questions, observations, or other information that might not otherwise come to light. There are some significant deficiencies, of course, but I think works fairly well depending on the group.

Where it breaks down is if one person starts to dominate the conversation for the duration of the class and carries it off-topic, or if someone becomes combative. So, the group composition and personalities can influence the relative success.