In the world of pump guns, you are always better off spending more for a Model 12, IMO. The Stevens were good reliable guns, but never developed the following that Winchesters, Remingtons, and Ithacas did. Kind of like comparing Ford Fiestas to Audi A4's. Both will get you from A to B reliably, but which would you rather own and drive? Shuck a Model 12 a couple times, then shuck a 520. You still see guys using M12's a lot, at club shooting and in the field. I can't remember the last time I saw a 520 being used. (Well, yes I can. My old man used one briefly back in the 80's, but even he, Mr. Savage/Stevens himself, went back to using an Ithaca.)
As for parts/repairs, any vintage pump gun is going to problematic in that respect no matter its pedigree, to one degree or another.
