Steve:
Some comments---
First: Chorine levels of .5 can be effective at keeping a clean pool clean, but nobody will claim it will clean up a dirty pool. (except maybe N2)

Second: .5 is ONLY effective with no CYA in the water. The Best Guess table is an empirical table showing effective maintenance and shock levels of chlorine for various CYA levels. So it's really irrelevant in the real world to discuss .5 chlorine levels. Most people who follow pool store rules are d*** lucky not to get algae when using pucks and keeping FC that low. Actually, many of them get algae, and finally come here for help. I'm inferring that your point is that N2 is leading people down the garden path to serious water troubles. I agree with that.

Third: I know that silver can be an algaecide, but that doesn't make it a sanitizer. There's a difference. I'm guessing that at levels where it can actually sanitize (kill microbes) is definitely not safe for human swimming.

Fourth: I, too, argue that simple arithmetic tells you that the N2 isn't worth the money. Now the seasonal cartridge is over $100. That buys a HECKUVA lot of chlorine--and you need to buy chlorine with the N2 anyway. I'd bet $100 that 999 out of a 1000 pool owners don't save that $100 in reduced chlorine usage.

Fifth: N2 uses that bromine and bacquacil producers' myth that chlorine is irritating and lots of people are sensitive to it. We know that's not true--properly maintained water doesn't irritate most people, and the few it does have explicit medical issues.