I have used them to put primer and paint on small parts. I primed my engine compartment with a preval and ppg primer one panel at a time and just worked my way around doing a section of it each weekend until it was all done.

They get cold and stop spraying smoothly if you use them continuously so you'll need to spray in bursts rather than holding your finger down the whole time. If your paint is thin and has lots of metallic it may not come out all that great just because a preval can't atomize the paint like a real spray gun can.

You may be able to spray the color on one panel at a time using the factory edges as stopping points and then carefully backmasking the edges when you start in on a new panel so you don't end up with tape lines that tend to lift later on.