I have the replenishment unit (2 of them actuallly), its' a great addition to the CP-31. Personally I would not be without one - it's really critical to keeping chemistry topped up and fresh, and is such a nice unit that it's worth seeking one out. FWIW, I have found you can crank the replenishment rate quite low and still get great results. I think it has 9 settings, each is 5ml greater than the last. I have mine set on 2 (out of 9) I believe and it's quite conservative in chemistry use, but also still allows great results.
I'd be a bit concerned if sharing this unit with others - They should be trained in it's use and particularly in care and cleaning of it, if you want to get a long life out of it. Replacement parts are expensive. Using it carelessly can result in paper jams, chemistry contamination, etc.
for example, I'd hesitate to set up something like this where it would be used unsupervised, like a college darkroom or somewhere like that. It does require some care and feeding and careless use and not cleaning it regularly will result in sub-standard results and a short lifespan. It's too nice a unit for that kind of abuse... ;-)