No disrespect but as in Childrens panels, such circles will be a magnet for the "do-gooders" in society and no matter how well-intentioned they may be they are among the most easily deceived.
I understand your point very well and it is a good one. Some prisoners will 'play along' in prison. That is understood as par for the course. However, some of the people involved in trying to make a difference will be abuse survivors/victims and the others making up a group, all of whom have to be selected and trained, should of necessity be shrewd and 'down-to-earth' types (as specified) individuals so the right level should be achieved.
I do know what you mean by do-gooders who can be ineffective. Quakers themselves are not known for being ineffective in Prison Reform, Abolition of Slavery, reform for Gay and Lesbian Rights and many other movements. On the contrary.
There was an instance given by me on this thread of where Circles of Support has worked very well in Canada. (Originally started by Mennonites.)