[Ryland]

That gun you linked to is the exact gun that I have.
The valve on the gun is at the tip of the 8" long metal tube so you can let foam goo build up and dry and a wire brush or rubbing it on a chunk of wood will clean the valve/tip off in a matter of seconds.

I currently have a can of foam on my gun that is over 6 months old, I've used little dabs of it here and there and it works great, I have a can of gun cleaner too but I only plan to use it for long term storage of the gun, or if I wanted to sell it, the outside of the gun is all nickle plated brass and steel, with Teflon in a few spots so nothing really sticks to it for very long.

I've taken for granted how well the gun works compared to the cans with the plastic straw until I was at my brothers house filling a few holes with a plastic straw can that he had, those cans feel like they are either on full blast or 95% off, so laying a 1/4" bead of foam around the edge of a sheet of foam, or sealing in small gaps and cracks can be done very easily, mine also has a trigger stop that you can dial in and out so the trigger stops at a 1/8" bead, or 1/4" bead or 1" bead even or crank it all the way out and you can spray a foot or so and get a large void filled, altho it's a bit wasteful to do that to much, but the trigger is smooth and easy to maintain control with so you are not wasting foam.
I have not done a side by side comparison, but I have a single can of gun foam last a long time, feels like 4 times as long as a plastic straw can even tho it is only twice the size, most of this is because of the control you have over the flow, but it's also because on the gun the can is sitting upside down so you get every drop out of it and if you only use half a can next month you can use the other half.

Also, with any kind of foam like that, cover your hair, wear old cloths and rubber gloves, this foam takes almost a week to come off your skin.