I'm not sure how effective it would be with an abusive parent, or a bully. I suspect not very.
I think a lot of elementary/preschool teachers are ExFs, so they might think this is awesome. But, thinking about how it would have made me feel, doing it in front of the whole class would be terrifying. I like to keep many of emotions relatively private, and will not discuss them with anyone, in any context. This isn't because I'm afraid and need "growth" to realize that I can say what's on my mind, but rather because I have found that many people are poorly equipped to deal with my feeling stuff because they are intense, and not something people can empathize with to begin with.
As a kid, I think it would be even worse, because adults have a way of assuming that all kids are the same, even though they aren't. I can also see a lot of "no one is wrong, there are just different points of view" stuff that no one truly believes, and worse, denies that in conflict situations, sometimes one person can truly stand out as the asshole. I can see a lot of fake "impartiality" that is really nothing more than wanting to avoid making a decision and hope that the problem takes care of itself. I'm kind of extrapolating from the examples given to situations where this method is tried where there are conflicts between students.
I mean, it's better than "stop whining about it, you're 6 years old and a man now", but it doesn't seem like a perfect solution.