I have used both and prefer the Duragloss. You'll hear the opposite about as often. I started with the Flexcoat on rod #1, then moved to Duragloss for my second project and did much better -- probably in part because I was more experienced the second time around. Since then I've worked out a method that never lets me down.
there was a product called "Duragloss 2000" that was too thin, though I've not seen it on shelves at all lately. It came and went pretty fast.