I could not get the penny to seal - the alcohol would drain into the bottom before it started boiling. I replaced the penny with a short, fat screw (something like a #10x1/2") and it works great. It builds more pressure than the double-wall design.
Also, I have found that Pepsico cans are too thin and split easily. Coke or Dr. Pepper cans work okay. Those high-dollar 16-ounce energy drinks are even thicker. I'd rather empty a Heineken can than any of the soda, though.