I tried the flame spreader once. It didn't work all that well.
I had caught a ~11 brook trout and had him for supper. I poked a forked stick through his mouth and spread his ribs near the tail section. Using an rusty can lid as a spreader I cooked his tail, then slowly moved to the front. Took about 20-25min. It works better over a fire when you can have a few fish over the fire.
I now have a small frying pan about 6" in diameter with a cut down handle and weighs about 6oz. I add a squirt of oil and some salt, frying them in two pieces. Takes less than 10min for two fish. If I don't bother bringing the fry pan, I just cut them into 1" steaks and poach them with some spanish rice.
The bones are a pain. Often, I will walk into the woods a hundred yards or so and bury them rather deeply (8-12".) Otherwise critters may come to see what you are about for supper ('Coons, fox, coyote, bear, etc,) then wash my pot/pan and hands/face. I am guessing that mice and floor dwellers dig the bones up and eat them eventually…