I'll chime in here. I'm extremely biased, but only because I've been shooting paint and coatings since the Johnson administration. Here's a link to some of my finished pieces ...
viewtopic.php?f=8&t=16855Single action or dual action? Dual action of course, because of it's versatility. Only the DA allows the operator to variably meter the amount of liquid paint entering the air stream, while on the fly. The user can shoot light dry paint films, or heavy liquid films simply by easing the index finger forward or backward. What does that really mean?
It means that by simply wigging your finger one can quickly shoot a uniform liquid film as seen on the black sub base coat of this 33 Willys project ....
(the fluid lever is pulled back, allowing maximum fluid to be metered)
... or direct paint so gently that the atomized droplets or flakes can be counted as they accumulate ....
(the lever is only partially opened, allowing pinpoint control of minimum liquid)
....and then one can switch back and hammer the clear on in successive liquid coats, as quickly as you can change the spray cup and flush the nozzle.
( lever all the way back delivering maximum materials)
Dual action simply refers to the function of the "go button" or fluid lever. Action one is pushing down and and engaging the the preset air pressure. The brush will start to hiss as the air escapes around the nozzle. No paint will flow until you ease the lever back, which would be action two. The farther back you pull the lever the more liquid paint is allowed to enter the air stream.
For example:
The gold metalic color base is shot with the metering lever pulled all the way back. The dark cherry metallic is worked carefully up from the edges with the fluid lever barely engaged. The gold frost is shot over the top with the lever a quarter open, using an exaggerated spraying distance. It is lofted over the top and allowed to accumulate slowly.
The emerald green metalic is applied like the cherry at the bottom, only it is worked down from the top using no more than a quarter of the lever's available travel.
Once the deeper emerald was color built to taste, I switched to lime ice metalic and frosted the entire model from distance using a quarter of the lever.
There is no real comparison between the two designs, other than they both shoot paint. In order to paint well, one must be able to regulate air pressure, viscosity, and liquid flow. One design is varialbe, the other just blows paint at a comparatively fixed rate. I prefer siphon feed to gravity feed, because it allows quick material changes on the fly, while one is still in the flash window. While I fully appreciate the top loaders, I find them to be a bit messy in practice, for what I do. I do a lot of wet on wet application, so timing is critical.