As long as you don't go to nuclear physics, they behave essentially the same apart from the small weight difference. Conductivity, magnetism and so on is all determined by the behavior of the electrons which don't change here.

The isotope ratio of iron is essentially the same everywhere for the same reason: There is no natural process that would separate them or even accumulate one isotope much more than the other. No matter where you get your iron from you'll have 5.85% of Fe-54 and 91.75% of Fe-56 with only really tiny variations. Artificially you can separate them, if you absolutely want a sword that's 4% lighter.

For iron no one cares, but for uranium these isotope ratios are closely monitored to make sure no one steals it or tries to extract enriched uranium or similar. That's why it was a big deal when uranium from a mine in Oklo had just 0.6% uranium-235 (the main isotope used in reactors and nuclear weapons) instead of the normal 0.72%. Did someone steal something? Turns out this site had a natural fission chain reaction two billion years ago, reducing the amount of U-235.