Indeed, they'd surely do their best, I'm convinced of that too. However, if it were a matter of determining whether a doctor had made a medical error or an electrician had erred in his work, I would want to hear the opinion of experts in the field in question.
I haven't made up my mind about this yet, but it does surprise me a little that non-lawyers could determine that there has been a miscarriage of justice. I'm a lawyer myself and I find this somewhat surprising. I wonder to what extent the fact that an ordinary citizen sees decisions being changed by non-lawyers can undermine the credibility of the commission.
I understand you have no concerns in this regard