I have a Primus Micron and have had no problems with it at a simmer setting. I've heard that the same is true with Snow Peak stoves. It helps to use some kind of a windscreen (being very careful not to overheat the canister!). The windscreen also keeps the canister warm (without overheating) on 20*F mornings.
I think the "4-oz." canister refers to the amount of fuel. The gross weight of a 4-oz. MSR Isopro canister is 8 oz. (MSR is kind enough to state both on the outside of the canister!) My Primus Micron stove weighs 2.5 oz. I can therefore go out for 6 days for a total weight (stove plus fuel) of 10.5 oz. I defy you to do that with a Whisperlite and metal fuel bottles!
Your right, no way i could do get a white fuel that low.
I just went and picked up some new toys!
a Soto Micro-regulated stove, a GSI Dualest Kit and the 230g fuel containers. I'm truly in love with this setup. I took one of the lids off of the small cups and every thing fits inside the duelest kit. Oh and i took out the crapy sporkes. really I could do with only one cup and lid. I cooked a round of pasta in it for dinner and it worked great. simmers super nice. doesn't heat up as fast as the jetboil but thats to be expected without having the heat exchanger on the bottom of the pot. all together with the larger fuel canister (i call it the med sized one at 230g) it weights in at 21.30 oz where the jet boil is 23 oz with just 1 100g fuel container. 2x the fuel for 1.7 oz less. not bad.