Duplicolor or Summit paint?
I believe the material Summit and Eastwood sells is a Kirker product - relabeled. Duplicolor is lacquer based. That's why is simple and easy to use. Of the two I'd go with the Summit/Eastwood/SmartShoppers material for shine and durability. It's a urethane. The cost is on par but still less than your PPG's, Sikkens, BASF - all of which are outrageous.