It's a third-gen .45 auto. It was from S&W's "value line" which forego some cosmetics to bring pricing down. Accurate, reliable, easy to shoot, and with the 457 the alloy frame makes it fairly easy to carry.
The sights are plastic, and are an odd-ball size dovetail, so you can't just stuff in metal 3rd gen sights. Grips, mags, most inside parts, etc. are the same as a 4513. The gun will fit many holsters made for a Sig P229.
They make an excellent carry gun because of the fine combination of weight, capability, and above all price. I'd say $425 is a good price, depending on condition. I think the price is starting to climb slightly on these as people figure out they are a great value. I don't think they're going to skyrocket any time in the future either, but at $425 it would be hard to loose any money on it right from the start.
I have had one for a few years and love it. They're truly a hard gun to beat overall, and still sorta a sleeper.