The efficacy data says "The product must be used in conjunction with an EPA-registered source of chlorine (such as Chlorine Bac Pac)." They amended the registration for use in spas and bromine may be used in place of chlorine. They did their actual tests using the equivalent of what would occur from the use of bromine tabs (BCDMH) with their product with 1.3 ppm BCDMH with 2.6 ppb silver ions. The lab results supported use of the Spa Frog with bromine in the 0.9 to 2.25 ppm range. The EPA approved their label which has 0.5% silver chloride as the active ingredient to claim disinfection and the use of chlorine or bromine at 50% of the levels they would be used at by themselves. So instead of 1 ppm FC or 2 ppm bromine, it's 0.5 ppm FC or 1 ppm bromine. Note, however, that their claim that it reduces chlorine or bromine "use" by 50% is only true to the extent that ALL chlorine or bromine loss is from sources proportional to their level such as loss from sunlight or oxidation of fixed amounts of chemicals or surfaces. So IF one maintained a lower chlorine or bromine level in an outdoor residential pool, then one would use less chlorine or bromine. HOWEVER, silver ions (unlike copper ions) do not prevent algae growth so in practice one still needs to maintain a chlorine or bromine level sufficient to prevent such growth. For chlorine in an outdoor pool, this means an FC sufficient for the CYA level and that level will not be lowered at all by the presence of silver ions. The loss of chlorine or bromine from killing bacteria is too small to be measurable in test kits.
In a spa used every day or two, it is the bather load that determines the bulk of the chlorine or bromine usage, not the minimum level of chlorine or bromine that is to be maintained. So there will be no savings when using silver ion in a frequently used spa. In a spa used infrequently, once a week or less, then one can maintain a lower chlorine or bromine level so could get a modest amount of savings in usage.
So for an outdoor residential pool, there is no savings from using the Frog. If one wants to spend more to have "savings", then one can use an algicide. Copper ions would work to prevent algae, but can stain pool surfaces and turn blond hair greenish, but Polyquat 60 weekly would also work and let one have a lower FC target level relative to CYA and therefore save on chlorine. However, the cost of the Polyquat exceeds the savings in chlorine so this is not normally done. It only makes sense for those who want a lower active chlorine level in their pools and are willing to pay for that possibility.
By the way, silver ions can most certainly stain pool surfaces (mostly plaster) and they are very nasty black stains. This is why the silver ion level is kept so low and why pH also needs to be controlled so that it doesn't get too high.
I'm missing the point of the Pool Frog discussion in this thread. It doesn't provide any practical value so why is it being discussed? The only benefit of having the silver ions in the water is some level of "insurance" if the chlorine level gets to zero since uncontrolled bacterial growth will be somewhat inhibited. However, since it won't prevent algae growth it's really not that great insurance.
