The GS-100 is definitely a very nice little stove. Very solid. It's not the best at simmering, though, is it?

Interesting that the kettle lid fits the GSI cup. Generally, in terms of efficiency, you're going to be better off with a wide, short pot than a narrow, tall pot. If you see the flame going up the sides of the pot, that's wasted heat.

The basics of stove fuel efficiency:
1. Turn it down! A low flame is much more efficient. Avoid flame "spillage" where the flames go up the side of a pot. For this reason, a wide, short pot is generally better than a narrow, tall pot.
2. Use a lid. Escaping steam = escaping heat = wasted fuel.
3. Use a windscreen. Not using a windscreen can result in up to a 300% increase in fuel use -- or your pot never coming to a boil.

You can also use things like post cooking pot-cozies where you turn off the flame, take the pot off the stove, and put the pot into a cozy to keep it warm. The contents of the pot will continue to cook, but without using any fuel. A heat exchanger also adds to efficiency, but a heat exchanger is sort of the "icing on the cake." Use the basic three above first.

HJ