"Is is worth it to use a Ransom under such conditions?
Isn't the value of the thing the absolute repeatability?"
You can still use a Ransom but you need to mount in on a base and mount a scope on the base also.
I actually have a piece of 1/2 inch Al plate that the Ransom is bolted to, along with a piece of 1 inch off to one side about 10 inches high that carries a scope.
Some benchrest type leveling screws allow the baseplate to be retured to the same spot on the bench if it does move, and the scope allows for very accurate sighting.