They're just fish; nothing extraordinary about them....except for the fact that some people who aren't allowed to keep them have built up a mystique around them strictly because of that. But if they are common and cheaply available...and if someone intends to use live feeders anyway, which is a whole separate topic...why wouldn't they be useful in that role?
Just look at a typical Channa...or, for that matter, an Asian arowana. No spines...elongated, slender, flexible body...these things look like they were designed to slide smoothly and easily down a predator's gullet.
Human nature being what it is...the most valuable and coveted element on Earth is and always well be...unobtainium.