Well I think that method works better than yours. Who's to say slamming a fish on the ground works the first time? I bet it doesn't. You have to be sure you do it right or the fish will suffer. With the freezing method it is proven that fish metabolism slows down, like lots of animals, and they sleep. How do you think native fish survive under ice? They are alive but really asleep. Temp drops a little more they die in their sleep. Your method is quite stupid because it is not 100% to work each time, I bet the success rate of killing a fish that way on the first slam is very low.