I was skeptical, but had success, here's my story... one purple tang with ich visible, other fish had no signs (2 clowns, flame angel, dottyback). Got the tang out, into TTM with the plan to catch the others, TTM and add all to a hospital tank and go fallow. This plan got cut short, couldn't catch the other fish, and ran out of time for a complete breakdown as I was going to be out of town shortly.
So, kept the tang out for a month, he got healthy and fat, no signs of ich. Was going out of town for a week, and needed him back in the main tank for the autofeeder, knowing he'd likely get ich again even though the other fish still had no signs. Sure enough, once back in, signs of ich within 72 hours.
Now, I had a choice, try Polyplab Medic, or take out all the corals and rocks to catch the other fish (dottyback was going to be impossible otherwise) and go fallow as originally planned. I have some extended trips coming up, so I figured why not try Polyplab Medic, and then fallback on teardown after my trips.
After I started using the medic, the visible ich (trophont) slowly decreased as they dropped off, and no new trophant to speak of. After about a week, the purple tang had 0 visible ich.
Completed the 3 week treatment, admittedly missed a few treatments. One week since completion, and still 0 signs of ich. It's only been a month so far, but fingers crossed... I know there are likely tomonts lying in wait, so only time will tell but for now I have happy & healthy fish.