Here is what Consumer NZ reported on the SimpleSilver product
https://www.consumer.org.nz/articles/legionnaires-traced-to-spa-pool
We do not recommend Simple Silver for use in a HotSpring Spa. Our Hot Spring Spa Models are factory ready for our Zodiac continuous Silver Ion Cartridge system to be used in conjunction with an approved sanitiser (chlorine, Bromine, MPS). These producst are safe and effective in Hot water.
The Highlife and Limelight range spas have 24/7 filtration with either 24/7 ozone water treatment (continuous sanitation) or Automatic salt Chlorinator. Other brands have Intermittent Ozone with programmable water treatment and either the Frog Automatic dispenser or manual adding of chlorine, Bromine, MPS following each use.