It looks like there is some ambiguity around the mass of the water and oxygen recyclers (higher mass to prevent a cheaty feel / lower mass to make it more usable). If we use the smaller CO2 scrubber and water purifier (5 tons and 3 tons respectively) instead of just sending more oxygen and water, the approximate break-even point is a crew of 7 going to and from Jool. If we have less crew, or are going anywhere inside Jool orbit, it doesn't make the recyclers useful. Add in their need for electricity and it hurts a bit more. Maybe it's the simple idea of avoiding waste that's appealing, but making the recyclers lighter would make them desirable for interplanetary ships instead of limiting them to bases and orbital stations. There was a blurb in the calculations spreadsheet about making them 0.75 tons when empty, which may not be a bad starting point. After doing a lot of digging around in NASA articles I could only gather a gut feeling that the CO2 and water scrubbers on the ISS would be in the hundreds of kilograms range (not thousands), but that's without any added infrastructure, and it's also for human beings instead of Kerbals. I feel torn on this.