Cube is good size for indoor rearing of cats. The large drop down front door accommodates large cuttings and makes cleaning and maintenance easier. It also makes for an easy exit when the butterflies finally take to the air. The 15" cube provides good ventilation and plenty of space when they emerge. The cube design keeps the cage stable so it isn't likely to tip over unless disturbed by wind, pets, .etc. Had good success with it as I just released two butterflies yesterday. :-) I do use a smaller container when the eggs first hatch, then move to them to the 15" cube when the cats are big enough to see easily.
I got both ebooks because this was the first time I had decided to grow milkweed and monarchs! There is some valuable information in both books that has helped me successfully keep my milkweed thriving, and also get my monarch butterflies to survive through eclosure! Very grateful for the easy to understand writing in the books, and the author's knowledge!