The bigger differences between most of these reproduction offerings is shape on each of the leaf ends, the shape of the top leaf where it installs into the crossmember, the tie-bolt shape, whether it has a bushing in each eye, -and if so, whether it has been reamed to the correct size for the spring hanger (shackle).
As far as the spring steel is concerned, where do you suppose all of the spring steel is manufactured? Maybe a different way to ask this is, where is spring steel manufactured in the US these days?
Bottom line is, you can buy the cheaper $$ springs that are reasonably close to original in form & function however directly out of the box they still require work to be usable, -or you can pay more $$ for a spring that has those additional 'ops' done to more closely replicate the original spring in aesthetics, --or you can potentially restore an original spring whose steel composition is arguably superior to what is used on the reproduction springs today. It really just boils down to what your goals are.
