"What is the point of the folds?"
Well, after experimenting with the venturi stoves I found that the folds actually allow some air to be drawn into the stove similar to the left hand stove in the pic. The one pictured has been burned about 30 times before I took the picture. It apparently works well enough to keep the sides from discoloring. I made several others that had 1-5 holes in them about two thids of the way down. 2-3 seemed about best for improving heat without overheating.
Trail Designs 12/10 is a chimney stove very similar to the older Brasslite. It is not just a top holed stove. I made several versions, some taller about the same width. Some narrower and taller, some shorter, some shorter and narrower. Adapting the simmer sleeve from the older Brasslite (from a strip of aluminum) it functions about the same with fair to good flame control. Outside air is fed into the burner from the bottom, along the sides and out the top. Brasslite used solder and an inner and outer wall. The 12/10 uses some sort of high temp adhesive to seal the bottom of the inner ring, or perhaps a smaller can. The 12/10 also uses a series of holes as air inlets. This was avoided on the Brasslite, simply using a slightly shorter inner wall.
The Mercury stove uses nothing inside. The folds form a sort-of venturi that burns with good to excelent efficiency and only weighs about 8-9 grams. The 12/10 weighs about 17g. It works in the CC fairly well at about the same efficiency.