Hi, I've used the Wagner spray gun (same model) for painting a radiator and managed to achieve quite a respectable finish (it was much better than I expected for what is quite a cheap piece of equipment). I was using water based paints only so I don't know how the finish would be with oil based paints. I wouldn't use it to achieve an ultra fine finish or use it on any of my cabinet work.
I'd say that the following helped to give me a reasonable finish:
1. use the viscosity measuring device to check your paint. In all likelihood the paint will be too thick (for the emulsion I was using I ended up using 2 paint to 1 water to get the viscosity just within the recommended level). You'll need to do a bit of experimenting to get the right viscosity but it's essential the paint is sufficiently runny.
2. apply using lots of thin coats (I ended up using four applications for the emulsion and three for the special radiator coating on top).
3. test the sprayer on some cardboard before using to check on droplet size. I found it worked better toward the finer droplet size (but not mist!).
4. occassionly you might get some big droplets spitting from the nozzle due to paint collecting around the nozzle - happens if you stop spraying and start again, so worth checking and giving wipe.
If in doubt have a practice on some scraps of wood to see how it turns out.
Hope this helps (and good luck).