Roux the day... in a jar

So last night I was watching Alton Brown make gumbo on "Good Eats." He went through his way to make a roux. I've never had that much difficulty, but it brought to mind something I saw in Winn-Dixie the other day: roux in a jar.

I've heard of it, but I've never tried it. The purist in me wants to be against it, but....