The only thing I would be worried about is the replenishment rate. It's based on a gallon of working solution, and could be different if you only use a half gallon. You might get fairly large fluctuations in activity that way.

But why not try it? I print enough that I spend all of the replenisher before it goes bad, which is very well within the six month mark; I probably use a gallon kit every 8-12 weeks.