I would opine that these guys have their head in a dark place, and in my mind it makes all their products and advice suspect.

Antifreeze has is own carefully blended mix of chemicals that function as corrosion inhibitors, and it's best not to introduce any other chemicals. This is best done by blending distilled water 50/50 with antifreeze. Soft, potable water is usually okay with most OEMs, but distilled water is best since it minimizes the introduction of minerals or other "contaminants". Chlorine is especailly bad!

Some racing organizations disallow antifreeze in cooling systems because it is hard to clean up spills. In such cases soft tap water or distilled water with a proper dose of a commercial corrosion inhibitor formula is the correct choice.

Of course, for a normally driven highway automobile, you should run a 50/50 mix of the OE recommended antifreeze and (distilled or soft tap) water. The corrosion inhibtor packages that are part of all commercial antifreezes are as important as their freeze and boilover protection.

Duke