The metal is lead-free pewter with a little silver in the alloy. Like said, very malleable - you don't want to drop it. I have known one bari player who found an old D8 to be good on an early Chinese low A bari. It sounded normal, not too bright, with a deep, round tone. it really depends on how you play these baffled pieces as to whether it will be 'bright' or not, plus it takes weeks to bond with a mouthpiece and begin to sound like yourself with it.
As for 'corrosion', wash the mouthpiece fairly often and never leave a reed on it when you're done with the sax. You can use any metal polish on it at any time to make it look new again if you wish.
I'd say if you can get it at a good price, you could get your money back by selling it if you don't like it. The main thing is condition - has it ever been damaged? Is there pitting on the table? Any dents on the shank end making it out of round? Any dents on the tip or rails? Its hard to find one of these used that is perfect - the question is, how bad is it?