NEVER, NEVER, EVER, leave the cockpit with the engine(s) in gear and you won't come to more harm than a short swim.
I now break that rule on the lifeboat but I do have wide decks and a very high rail, I never broke it on other boats, and particularly not on my little Fred Parker, which I did fall off while putting out the fenders by Moodys yard, but following rule one no harm came.
How many of us actually use this? I admit that I never do as I think the risk of falling overboard whilst sat or standing at the helm is minimal, and I would have thought it would be impractical to do this single handedly.
However I do always fit and use with the dinghy outboard.
Hmmm, with smaller fast planing boats (24 footers for instance) now being fitted with new generation diesels I would have thought such a device could be considered valid (a fuel cut off trip switch for instance).
I had a sports boat once, with no proper rails. I got a proper bow rails built to stop the wife falling in when anchoring. Mind I still lost her anyway!!