FWIW: In my opinion most of this discussion about efficiency and all of the associated physics is interesting but largely irrelevant, to me at least. On my typical bike tour I really don't care about getting all of the heat into the food or using the least amount of fuel possible. I figure that when I can get fuel frequently and in smallish quantities, I am just not going to worry too much about using a bit more fuel.

If I can simmer at the cost of being a bit less fuel efficient, that is fine with me. I have not used a diffuser, but it looks like a useful item to me. I don't know if I will start using one myself, but I can see where they could be a plus. I guess that it starts to look attractive to me if it weighs less than a second burner specifically made for lower output (about 0.25 ounces).