You are correct Tony, and it's important that people understand that.
The Epa tested Spa Magic in 1991. Which was about the same time they were examining dioxin and taking a beating from DOW on chlorine phase outs brought by the 1993 Clean Water Act. They found Spa Magic, when used properly, worked better than chlorine and bromine by eliminating all harmful bacteria while chlorine and bromine only maintain them at 'safe' levels. However, Spa Magic only has a shelf life of 5 years, is only effective at temperatures of 90+ degrees and will last 3 months for most hot tub users.
But sometimes, Shtuff happens!
This might not be the best example to make a point but heregoes: Imagine parents go out of town and their teenager have a party where a dozen or so people get wild in the tub with drink, food and a convenient place to go to the bathroom and everything gets turned off when its over. Any bacteria that wasn't killed before the water cooled could be multiplying at a rate of 200% per hour at temps between 45 and 90 degrees. Spa Magic doesn't begin to do it's work until the temp reaches 90 and the water doesn't have to appear dirty or even smell to be harmful for several more hours or even a day or more. Ecoli, even in a properly chlorinated pool, can remain undetected and deadly for more than a day.
By adding the proper amount of spa chlorine sanitizer (Sodium Dichlor 56% available chlorine) and running the jets with your cover off and water at 90+ degrees for an hour or so, you could quickly drop the bacteria count to a safer level boosting the effectiveness of Spa Magic as the chlorine gases off.
Using a garden hose that has sat outside in damp conditions can infect your water in a similar way when adding water to the tub.
Silly story I know, but I've heard too many people say they use and love Spa Magic and plan to never use chems again. But if shocking a hot tub is all it takes to eliminate risks that may not have been considered, it's worth the little effort to be safer.
You can read more about Spa Magic at chemfreespas.com