In my opinion, if you are going to sell these scales, I would sell both pairs. If they are vintage, they should be worth quite a bit of money. Collectors like to collect these things. Plus, it's old stuff. Progress is never slow, and you could buy a
cheap smart electronic scale that could perform a lot more functions than these vintage ones. Of course, the choice is yours, but if I were you, I'd try to make some money on it and use the profits to buy something modern and inexpensive that might also last a few years.