I have the Nature2 system, I disagree that it is too good to be true, Both My wife and son have blond hair and have never had any issues with green hair.
It does use metals to assist in sanitizing the pool, but I have not had any problems that people associate with that.
The cartridge costs $100 and mine last for 2 seasons, so it costs me about $50 per season, we use around 4 ozs of granular chlorine a week, plus you use a "spring" cartridge for the start up at the start of the season it costs about $24.
Always have sparkling clear water it is softer as the Nature2 does use minerals.
Most people will advice against it, but I am a fan of it and I don't have any issues with my water.
I am speaking from my own experience with the system and that fact that I do not have any problems with my water chemistry, green hair, algae or metal staining.