Hi all, Does anybody here use this Sigma 17-70mm F2.8-4.5 DC Macro lens? Are you happy with it? (I might buy one from someone who bought it used in August and has been trying to sell it since December. He's asking for $225, and the lens seems to be in perfect condition. It's just suspicious to me that he's willing to sell it for almost a third of its cost.) Thanks for your help!