I am far from being an expert, but hope this helps. The Model 59 has an alloy frame. There are all steel versions, Model 559'S and 147A'S (rare) and all stainless Model 659'S. The all steel models weigh too much for my taste. I own an early blue Model 59 serial# range A17XXXX and I enjoy shooting it very much. I have two 20 round factory magazines to go along with the original magazines. Which limits reloading.
Being a retired cop, most police trade-ins were carried more than shot (we shot twice a year). Most guys including myself left (my) our service weapon(s) in our lockers when off duty. The guns should have been well taken care of, and fixed properly by the department armorer should repair be needed, so I would not hesitate to buy a police trade-in. The wear will be mostly cosmetic, which will not effect the shooting performance, and since you are buying the gun gun for shooting I say go for it.