those burners are more pinpoint. The broad diffuser on the Clevedon steam burner produces much heat on a larger front, and it's 28mm overall dia. I use it in my 3 inch horizontal boiler. As long as you silver solder the boiler, and your first cross tube is about 1- 2 inches from the flame, AND you keep the water level appropriate, AND you use the proper gauge copper tubes, you will have no problems. The whole boiler and its contents have to come up to temp before you get constant boil. I like a flame to heat the most area going down the barrel or through watertubes. I have used #8 and #5 jets with no significant change in time to boil in my 3 inch boilers (even allowing for O2 requirement). Copper is an excellent conductor of heat and easily conducts it away from 'hot' spots (eg: point heat on a crosstube), but efficiency decreases.
You of course realize that no burner is perfect off the shelf because as the gas pressure changes, the burner flame and heat changes. Appropriate O2 mixing and gas molecule distribution and gas mix are critical for best heat.
From net source:
Fuel mix (% butane/propane): Scorpion (100% butane), primus (75/25), outlander (70/30), isobutane (80% isobutane, 20% propane) and there are others...
Initial water temp matters too. Additionally, lagging, the flue design/updraft /smokebox/superheater design also important. But by far the most important element is your steam requirement. How much steam do you need for your project. The key is to design and build a boiling system to fit the requirement. Calculate need and then design boiler. Bench test burner/boiler designs for the best one for your application.
As far as crosstube boilers, these are proven designs with fairly quick time to boil, but not so much reserve.
