I'm not sure that I buy into the thought that a Jetboil conserves fuel, vs. other systems. I geek out over these things when I'm bored, and I've done numerous patio tests, and also casual field tests when car camping. I'm convinced that my SP giga stove with integrated wind screen, my JB Sol (aluminum version), and my new 1.0 L. Reactor all boil 2 cups of water with roughly the same fuel comsumption (between .20 and .25 oz. per boil). The difference is speed--the Reactor is really fast, the JB pretty fast too, and the SP Giga is slower. All 3 systems are good in the wind, and they all slow down in cold conditions. But they all still use the same amount of fuel to achieve a boil. Although I've not had the chance to fully test it, I'm thinking that the Reactor is the clear winner in high wind, and at altitude (>9000')
Then there's the issue of simmering with the JB stove burner. I think the newer stove, with its regulated output, does a pretty good job. I can reduce the flame output to a very low heat, moreso than with the original JB stoves. I can remove the integrated wind screen on my Snow Peak and simmer things nicely. Likewise, by using the JB pot support with a separate pot, simmering is easy.
But you can't simmer with the Reactor at all, since the heat output is so intense. 4 years ago I made a pot support to position a separate pot above my Reactor burner. It blew the circuit on the stove somehow (which can only be re-set by MSR), and I returned it to REI. MSR decided that I was a trouble-maker, and my pals at REI asked that I don't fiddle around so much, and that I should stick with the manufacturers' directions.
As for using the JB cup on other canister stoves, I think that the burner-to-pot-bottom distance must be considered. JB apparently has this optimized for their system. If you increase that distance, which will happen for most non-JB stoves, likely the efficiency will be reduced.
Weight is now the major factor for me, dictating which system I'll take on a given hike. The weights of my 3 systems, complete with a 4 oz. fuel canister and a MYOG cuben drawstring bag to hold everything, are as follows:
Snow Peak Giga------14.7 oz.
JB Sol--------------------18.1 oz. (without the stupid base cup)
MSR 1.0 L. Reactor--22.1 oz.
One last thing I should mention: when I did my muy frio patio cold weather tests a week ago, the JetBoil Sol seemed to actually do slightly better than the other 2 setups in -10*F conditions. Maybe this is due to its regulated output? Who knows...?
Edit--for spelling, before -B.G.- nails me.