Let me start off by saying no one has ticked me off, except maybe the companies such as Nature's 2. I was once (and only once thanks to Ben) a Nature's 2 patron. Here is MY problem with everything that has been said here as well as in the Natures 2 product manuals and web advertising.
In my opinion, the .5 residual of chlorine that is recommended would be used up faster than it could be replenished in a residential pool full of kids, swimming lets say from morning to afternoon. Then the average consumer would be relying only on the chlorine in the plumbing and the Nature's 2 cartridge itself to "sanitize". Ever got a toy in the skimmer? Granted some also have a main drain however I would venture to say that most people only have one form of intake. As Steve mentioned, forget about the algae. What about the "stuff" that chewed off the .5 residual in the first place. The average consumer probably wouldn't even notice the chlorine had dissipated until later that evening and by then, it could be too late. Now, throw into my little scenario that this average consumer has a CYA level of 90+ppm.

Dave