OK, so what's the downside of barn paint? Does it not last as long as
"better" exterior paints - or is it just cheaper because it's only
available in a very small range of colors?

I bought 5 gallons of white self-priming yesterday, figuring I'd do our
garage with it (which I'm hoping to tear down in a couple of years and
rebuild anyway) - cost me $60, and would have been around $300 for
equivalent "good" Behr* top-coat and primer.

There's gotta be a catch somewhere :-)

cheers

Jules