As a rule, gravity fed guns are much simpler to clean up after the fact as they have a very simple finish patch. Literally empty the cup, wipe it out as best you can with a paper towel, then add a few ounces of solvent (whatever solvent is appropriate for the finish), swish it around the cup and then feed the solvent through the gun to clear everything, wipe the cup one last time. And when you are completely done with the job (not between every coat) you may consider breaking down the gun just to verify that everything is clean (most of the time it will be, but the after-job break down makes it easy to ensure that no finish ever accumulates, especially for thicker finishes).
If you do not want to spray the solvent through the gun under power, then you can simply fill the cup with solvent and allow it to run through the spray gun under gravity alone (that is, with no compressed air). Some will use dirty solvent for the initial full cup rinse, then follow up with another pass of much cleaner solvent to finish the cleaning. You can save the finish to reuse a multiple times until it gets too contaminated. Use whichever cleaning style works best for you.
Beyond that I can not comment on the turbine systems themselves as I use an air compressor driven HVLP spray gun.