As far I know , the difference (aside the seals), is the pressure adjustment. Can be readjusted but for the price of the piece doesn’t worth the readjustment effort. On my car thought made the R134 “upgrade” on my stock system, including the expansion valve without any readjustment and worked really nice. But I will install a correctly adjusted R134 unit (same, 4 seasons unit that probably you got ) when reassembling my car.

About reuse the original one, well, my car was with the AC without any use by maybe 15-20 years by the original owner (and I refill the system maybe in 2005) and when I made it to work again, still with the R12 before the R134 upgrade, worked nicely.