I have been using Apollo HVLP systems for about 27 years. My first Apollo system was an 1100 turbine with 5000 spray guns.
A few years ago, I purchased a 1050VR turbine and 7500 atomizer guns. The only complaint I have had with any of the systems is with the 7500 guns. I spray different types of finishes, but I spray mostly oil base polyurethane. I had problems with finish backing up from the cup up into the cup pressure supply line. This is because the 7500 guns are non bleeder guns. Air only come out of the gun when you pull the tripper. This also turns of the pressure air supply to the cup allowing pressure in the cup & finish to back up into the pressure supply line. They have check valves to prevent this, but they did not work for me. I solved this by relocating the cup pressure supply line to a location to give constant pressure to the cup. No problems since. I have never read about anyone else having this issue, so it may just be the way I am using the guns.
The 7500 guns spray much better than the 5000 guns. I have never wished I had a different system.