Cast iron wheels with ribbed backs were used primarily before WWII. Wrought steel wheels (with smooth backs) were introduced in the 1930s and banned in interchange in 1958. While earlier modelers won't want to swap out their whole fleet, these ribs are quite visible on certain car types like tanks and hoppers. Kadee's products are non-magnetic and arrive in-gauge; I've not had a DOA yet. The plastic axles do make it a bit harder to add resistors for block detection, but not impossible; just don't try to solder to them.