The idea with the single-cup method is that the larvae are never in competition for food, and cannot stress each other. Also it allows for a totally complete clean-out of each container every day or two. I use a modified version of this. I keep 5-10 larvae of similar size per container, with no airation except for the open top. Each container is the bottom half of a 1-gallon plastic jug. I do a 100% water change daily (starting when they begin to be fed), and wipe out the inside of the container every few days. I return them to a tank setup when they are old enough to hunt down whole blackworms.
Amazing, the 100% water changes and pouring larvae back and forth among containers doesn't harm them at all.
I had a batch of Triturus larvae last year that were in a tank, and all dieing from fungus infections. When I switched to using this jug method, I had much better survival.
