I've always liked the freedom of human holders. plus as a holder myself I get that beautiful smell of pine just as the board breaks.
Even with accuracy one can hit the board holders. Assuming of course one breaks the boards first. I'd honestly be more afraid of hurting myself on the machine.
I agree with Falcon that even the most accurate people miss. I've never had a problem of hurting myself on a machine differently then I would have with a person. I did a spin kick and caught my heel on the side of the board which can happen with a machine or human holder.