That appears to be chamber capacity but do they address longevity of the chamber?
"One Full Salt Chamber 20 +- treatments" doesn't really address how long the chamber itself lasts. The manual also doesn't list the chamber as a field-replaceable part so if it goes out, do you buy a new unit or can the old unit be repaired?
I do notice, to their credit, a limited lifetime warranty. But that won't matter if you're in a situation to depend on the unit and it fails.
I have a daughter. I tell her, "911 is what you dial after you're raped. 1911 is what you should have before they try."