David,
I can't speak for Dave, but we like using the ball valves instead of gun's simply because we have more control, less fatigue and can work in tighter spaces. We never get trigger fatigue when we've been power washing for 12-14 hours straight because we never pull a trigger. It's also more versatile. We can use an assembly as small as a ball valve with a quick disconnect and nozzle for a one handed mini-wand that isn't more than eight to ten inches long from hose end to nozzle. Plus, you have total control over pressure coming out of the nozzle from right where you are working instead of adjusting the washer itself. It's also a lot easier to make field repairs using these setups. If we run into a bind we can run over to home depot or a local hardware store and put together a new ball valve wand assembly using threaded black pipe and a hydraulic hose covering it for heat protection for less than $30-$40 depending on the length of the pipe/wand we need. And they last forever. Think about it like this, how many times can you step on an aluminum wand or drop it before you crack or bend it? With black pipe it's heavier, but you can throw it against a wall or run it over with a truck and never have a problem.
As for your temp question it's never been a problem. There is a point in terms of pressure control where your burner is going to shut-off, we just listen for it and adjust the valve accordingly. One of the neat things about using the helmets with face guards and ear protectors that we have is that even though everything is muffled with the ear covers the burners have a lower range distinct sound that you can easily distinguish from everything else. So it's like you're standing right next to the burner even though you might be several hundred feet from it. After awhile you just learn where the pressure needs to be for the burner to be on or off.
I recommend you build one and give it a try, you'll swear off triggers and wands in no time just like we did.