In 2009 I bought a 93 K3500 that the previous owner had just used premade NAPA steel lines with unions, because the dreaded rear line had rusted out.
He put the lines on so he could sell the truck, so they were brand new when I purchased it. In 4 years, the brand new lines were again rusted out. I replaced every line on the truck with Ni-Copp, and 10 years later all the lines are still intact. At my age, they'll outlast me
.......LOL
Premium car manufacturers have been using Ni-Copp lines for a decade or so, even though they cost the manufacturer more to use them. It's really worth the extended lifetime of the lines to spend the extra money. I know my life, or someone in my family's life is worth the extra money, plus you'll never have to do the labor again because of rust, or corrosion from road salt.