Here is my update, for those who may be researching this product in the future.
I was using Kick-Ich. During the use, I didn't notice any clear adverse impact on the tank. With that said, I couldn't quantify its effectiveness (if any).
While using, I was concerned that I incorrectly diagnosed the cause and became worried that the outbreak was velvet, not ich, or some combination thereof. In a prior discussion with the manufacturer, they stated (and (of course) recommended) that I use their product "Rally" in conjunction with Kick-Ich. Rally apparently works against other pathogens, such as velvet.
I dumped the recommended dosage of the Rally into the tank.
The premise of both Rally and Kick-Ich, as I understand it, is to not kill the pathogens but to make it so they cannot attach to a host.
The Rally seemed to be doing something to my tank - my inverts (coral, in particular) started to retract and recede. After the second day of Rally and like the tenth day of Kick-Ich, the coral was looking bad and some of my fish seemed to be doing pretty bad also. Consequently, I ripped my tank apart to get my fish into a QT to treat with copper sulfate and did a major water change in my main display tank.
Most of my fish, actually all but one, didn't make it - I waited too long.
With that said, in all honesty, i can't tell what (if any) impact (good or bad) the Kick-Ich had. I note that the directions indicates that continue treatment is needed until no fish have visible signs of ich and then continue one more treatment cycle from that point. In other words, it takes a long time to be effective. Two of my LFSs say it works but it is just diluted and takes a while (both LFSs sell the product).
In the course of researching this product, the manufacturer indicated that a public research facility in Florida has been using the product for years. I reached out to that facility, and the individual that I communicated with stated that they have been using Kick-Ich and another product (Hydroplex) for 10 years in all of their QTs. They weren't recommending the product, but just sharing their experiences.