I haven't used the Duplicolor rust barrier. I have used the Por15.
I think if you carefully prep as stated in the instructions, and follow up with top coat, Por15 is amazing stuff.
The problem with a new product is you don't know how it will hold up, even if it looks good now.
95 DGGM 396 Stroker, Eagle crank & rods, LT4 heads, LT4 intake, LT4 hot cam, Finish Line long tube headers, 2 1/2" exhaust, Big Baer brakes, 3.73 rear, Hotchkis lowering springs, Front and rear Hotchkis Sway bars, aluminum driveshaft, Metco aluminum boxed trailing arms, K&N, Gary's Cables, 42# Green Giants, T84's,T56 Magnum