I use this stuff at work (local to you actually, mermaid aquarium). It works rather well. I'm not too sure how it works but I think it attaches itself onto the nitrogen (probably breaking one of the oxygen bonds?) via one of the carbons (they state that it's an enzyme). Since the original enzyme is a surfactant, it gets dragged up into the skimmer.
But I guess in practical terms, it's effective. I've found that dosages don't really need to be too correct, as long as you dose daily. The reason for increasing the dosage is to promote a reaction ofNO2 to NO3, via le chatelier principle. After a while, no more reactants= no more products. I kept the system running as is, with ozone and everything. The only warning they really give is to be careful of your Alk and pH, which I would guess the H+ or one of the cations might also react with the hydrocarbon in the enzyme. The one time I checked, there was a slight drop in Mg levels, but nothing too offensive.
To be honest, I don't really even test the water or measure the stuff out anymore. I just squirt it in. I've seen no adverse affect so far, in terms of NO3. But admittedly, I need to monitor some of the other parameters more meticulously to confidently say there's no ill effects. Also, I use it as a preventative as well; so my NO3 never really rises too high.
I hope that helps. One of the better chemists out there should really check over my science though. It's almost 4:30 am and too much studying for me. I'm sorry if I gave any inaccurate chemical information. ::shurg:: pseudoscience... Anyway, hope that helps.