Graco is the most popular brand of airless sprayer among commercial painters. The early hand-held units had problems but I have heard that the newer ones are greatly improved. But I have not used them.
The spray tip on the Graco cordless model in the picture looks like the exact same tip used on the bigger commercial rigs. To clean, you simply reverse it by turning it 180 degrees and spray water through it for latex or solvent for oil based. Some airless sprayers are only for latex as they do not have an enclosed motor for spark control. I don't know if this is an issue with the Graco handheld sprayers.
I have looked for these handheld Gracos at rental places, but I haven't seen them yet. The cordless model retailed for around 1200 when they first came out, I believe, but I notice they are around 500 now. Worth the money if they perform well.
I would probably not spray oil based paint without thinning 10 or 15% or so. You may have a leveling problem otherwise, and the dry time will increase considerably. Latex, of course, should not be thinned when using an airless. When spraying a catalyzed paint like Matthews, mixing ratios for reducers and catalyst should always be followed.
Obviously, you can't paint a house with the handheld units, but if they perform well they would be great for coating out panels in the shop, and painting signs and sign cabinets and poles on location. It would be wonderful to be able to spray Matthews Polyurethane in the field.
Regarding moisture in the line messing up a paint job, a water trap should be installed at the compressor outlet. You don't need to spend a lot. Under 100 dollars. And if you have a run of pipe or hose from the compressor to the painting area that is not short, another separator would be a good idea at the spot where you connect your gun hose to the line from the compressor. A final filter could also be put on your gun. I used to use the plastic balls, but prefer the little glass/metal ones with the purge button on them. They last a lot longer since I was always breaking the plastic ones.
Note that some of the water problems can come from condensation in the hose itself, not just in the compressor, especially if the hose is in a spray booth that is unheated much of the time.
Brad in Kansas City