I've built and used these. Penny alcohol stoves are a popular "ultralight" backpacking option. They are so small and light
that even ultralight backpackers often carry two of them. With two stoves they not only have a backup, they can also can swap an empty, spent stove for a full one and keep boiling their spaghetti or whatnot while the empty cools so they can re-fill it.
The hardest part, at least for me, was pushing one can inside the bottom piece to stretch it out so the top half can slide in, then out again. The bottom kept getting stuck in the "stretcher" can. The other thing is the cut aluminium edges are sharp, so be careful!
The ones I have built don't have a patch of fiberglass insulation in them. I'll have to try that, see if it makes them burn slower and longer. When I use mine, I fill them to just above the dip in the well where the fill holes are, then cover the fill holes with a penny. (Thus the name "penny stove.")
Rubbing (isopropyl) alcohol burns cooler and is kind of sooty. "Heet" gas additive in the yellow bottle is pure methanol. It's cheap, readily available (we can find it in our local supermarket's very small automotive section), and burns hot and clean.