What intrests me, is the arguement that 'its natural' to feed feeders. I find that totally wrong. It may be natural, in rivers, lakes etc. where the prey has millions upon millions of gallons to escape to (I know some ecosystems are smaller, but you get my point), normally the prey has a semi-good to good chance of escape (with most fish people feed feeders to eg. oscars or other cichlids, they are quite inept at catching the fish, often taking quite a few lunges to get it eventually getting trapped between glass and the surface).
There is nothing natural about taking one fish, trapping it while a bigger fish chases it around. And I wish people would admit this, its natural for fish to eat other fish..in nature. Not four glass walls.
I would be quite interested, to provide feeders for a fish...In a 'fair' environment. eg. Having a 12ftx4ftx4ft tank, and what I would do is stock it as much as possible with guppies, give them a couple of months to multiply and build up a fair population, then introduce one small predator eg. a leaf fish so that the leaf fish could eat the guppies, but the guppies would have a fair chance to get away and the guppies will breed enough to sustain enough food. The guppies would get their nutrients from the food I would feed, so that way all the feeders will be high quality. It would be like watching nature in your you're house. It would probably work in a smaller tank like 8'x2'x2', as guppies are quite prolific and a leaf fish is quite small.