Interesting that Bell fit an overspeed system to a single. I believe that most singles don't have an overspeed system.
I was told that Bell 205's had a sytem and normal procedure was to pull the C.B so it wouldn't operate (ye of little faith) inadvertantly.
I suppose it's a balance of risk, which is worse an uncommanded shutdown where there is nowhere to land or an exploding engine if the drive fails.