I wanted to know how much difference does the heat exchanger on pot makes, and finally got around to do some tests.
Setup is as following, Brunton Vapor AF running on butane canister in liquid feed mode. Primus 1L eta power and alutech. Litech would be directly comparable but I don't have one, alutech feels thinner and lacks anti-stick coating, but that shouldn't make any difference.
Test was done inside to eliminate any environmental factor, each pot was filled with 300ml cold tap water and brought to rolling boil, in triplicates.
Weight difference (i.e. the weight addition of heat exchanger) between a 1L eta and litech is 23g according to Primus.
Boiling time:
eta pot alutech
3'30 4'10
3'23 4'12
3'27 4'20
Average difference of 48 seconds, 23% more efficient. While not up to Primus' 33% claim, it's not too far off either. I suspect on bigger pots with bigger exchanger the result would be closer.