Hi Hewy, I don't quite know how to answer your question. If you could see them, the mechanism is obvious. The slider valve has a large opening, ~3/16", the push valve smaller. The volume thrown by these flasks is determined by the nozzle size. There are also flasks with a push down mechanism that throws the amount of power set by rotating the nozzle end. There are also horn type flasks that expect the powder to be measured with a powder measure. There is no best single flask. I suggest that you purchase a few to see what one you prefer for your applications.