i'm by no means an expert on spray guns (or anything else for that matter). I realize HF purple guns are the bottom end, but they do have their place in the food chain. the basic "purple" has a lot of issues, mostly due to the quick and dirty manufacturing process. if you've ever taken one of these things apart, you know exactly what I mean. there's more sealing "goop" used in these things than you can shake a stick at. the crap's all over the place! enough said - if you're considering using one of these, COMPLETELY disassemble the thing and thoroughly clean everything. on reassembly, use blue liquid thread sealer, or Teflon tape on all, required threads (I use 1/4" tape - much easier for the smaller threaded components).
I've spent some time modifying a few aspects of the HF gun. kind of simple - basically, a detailed and thorough cleaning - I don't mean squirting some solvent thru the thing, but a complete disassembly and cleaning. also,
eliminate the internal regulator and most significant, a mod to the trigger mechanism that will make it a lot smoother and more precise. the trigger mod amounts to filing a flat on the needle pivot pin and adding a 5-cent nylon washer. the whole process takes about a couple hours, and you can end up with a fairly decent, special purpose, gun.
I shot some rustoleum thru my modified HF, and was somewhat surprised with the finish - laid down the paint like a sheet of glass. NOT saying it can replace your sata, iwata, devilbiss, or whatever, but for a cheap, somewhat disposal spray gun, IMO, it's not all that bad. not a production gun by any means, but if you're anal about cleaning, one of these things will give you years of service. I have some friends that use these things and achieved some pretty outstanding results.
my HF "not so purple" spray gun -