In my humble opinion it is priceless! I use one on all my setups. Not only do they keep you from having to constantly haul RO and add to the tank, they maintian the salinity at a fairly constant level through gradual replacement of the evaporation. Be careful to turn off the unit if you are taking water out of the tank for water changes, siphoning, etc or you may add to much RO though! Another benefit is to maintain the water level in your tank or sump at a constant level, this was critical for me since I am still using my old Coralife Skimmers which are really tempermental to changes in water level. They work great when the water level is constant though! There are a bunch of other units and devices out there if you search the internet. I just have had good luck with these devices.