Yeah, what Ned said, plus about $30 to $50, depending on the dealer. If you can get a 590A-1, get it, it's worth the extra $$$. If not, get the 590 and don't worry about it. I've got a 500, an 835, a 590-Security and a 590A-1, the A-1 being the newest, and the other three having seen several years of pretty hard use. I have yet to break the saftey or the trigger guard on any of them, and the difference in barrel isn't really a factor, as long as your not using it as a club. As it stands right now, if TSHTF, I'd grab my 590-Security, plastic parts and all first, simply because it has proven itself to me repeatedly - something my 590A-1 hasen't done yet, but only because it's so new that it hasn't had the chance to "prove itself" yet.
-John