I've gutted some...well, I worked on a trawler

Never saw this method, but might try it in the summer. I would think it only works on some fish or rather small fish.
BTW, a typical cod where I was fishing (N-Atlantic) would be some....15 lbs. And alive. We would basically put it on the back, cut in infront of the gills, then open um the belly, first at the chest, then cut backwards.
If it was a female, we would gently remove the "eggs" (Caviar) into a seperate container, then simply tear out the rest.
End result is a fish with no life and no guts...