I used this stuff last spring to clean up a bunch of brown jelly cyano that showed up on my rocks. I was after I got my JNS Cone CO-2 skimmer, I remember that, because I left the skimmer running with the lid off, and all the bubbles made quite a mess on the inside of my sump and stand. I started doing a bunch of huge water changes a few days after the initial dose, dosed again after a week or so, followed up with more huge water changes, and afterwards my tank never looked better. I also used a turkey baster and filter socks to blow off and suck out as much of the cyano as possible.
That was easily 8-10 months ago. No losses of coral (sps, lps and soft), no loss of fish, no return of cyano, and the tank is thriving like never before. I would have zero qualms about using it again.
I also have a ton of flow for my tank (somewhere in the range of 60-80x tank turnover via return and powerheads), so that could be part of why I had success (lots of surface agitation+powerful skimmer=very good oxygenation of water).