Jim has covered it well. Several members tried it with minimal or no results. The manufacturer even participated here on the forum for a short time trying to work with members to get positive results. When no positive results were obtained they stopped participating.
We have had several folks join the forum, say the stuff is the best thing since sliced white bread and then never participate again. I don't want to accuse anyone of being a shill, but these type of "reviews" are suspect at best.
We base our pool care system on accurate testing and only adding what the pool needs, when it needs it. To do that you need your own accurate test kit. Anyone who posts reviews of the product using only pool store testing (we have had a couple) are ignored entirely.
So, with that being said our advice is still to do a water exchange or a Reverse Osmosis treatment to reduce CYA. Water replacement is almost always more economical than RO.
People typically have 2 options to reducing their CYA (RO is not available in most areas):
1. Perform partial water replacement.
2. Add CYA reducer. Spend a week trying to let it work. Try another bag. Spend another week trying to let it work. Perform partial water replacement. SLAM because the pool turned green due to keeping FC low per CYA reducer instructions.