As Jason and Ike have said, you can search the forum and find plenty of threads discussing the chemistry of these systems in detail. The main claim that it lowers your chlorine use is incredibly deceptive. A proper chlorine level is dictated entirely by your stabilizer (CYA) level as that has the greatest impact on how much active chlorine (hypochlorous acid) is in your water. It is active chlorine that kills pathogens and oxidizes bather waste. It is true that metal ions do kill algae (copper) and certain bacteria (silver). But at what cost? You see, one of the main problems with these systems is that there is no way to measure how much metal ion concentration they are providing nor is there a cheap and easy way to test for metal ion concentration. So you basically are operating on the "dump & pray" method of pool care - dump in a bunch of "stuff" and hope it all works. That goes against everything we teach here on TFP. As well, the concentration of metal ions is important to know because it is what dictates the kill rates for pathogens - too little and the kill rates are much longer than chlorine alone, too much and you get very close to the point of generating metal stains. Metal stains, particularly silver stains, can be very difficult and expensive to remedy so, you have to ask yourself, is the "low chlorine" you use worth the risk of a damaged pool surface? Given the fact that you have a plaster pool, copper and silver staining is much more likely and, in the case of silver stains, impossible to completely fix (silver metal stains don't respond to any typical metal stain treatment chemicals and will require an acid wash to remove them).
As we always say here on TFP, you are free to manage your pool however you wish. But, the accumulated wisdom here on TFP says that those mineral based systems don't live up to their marketing hype and are more trouble than they are worth.
