The difference to me is how making a roux from scratch fills your house with a smell that can't be duplicated. That and how good a cold beer taste whilst stirring the pot.
I like the Green Onion Sausage from Bergerons in Port Allen, this along with Andoullie and Tasso. And yes, I use jar roux. Too easy. Now I want Gumbo. When I cook my rice, I drop a Boullion cube in it.
i love the jar and dont really care for the smell of a cooked roux (heresy I know) though i do eat gumbo year round. win/win for me. of course i dont like it dark as f like most of my coonass relative side. you're making some nasty creole gumbo?