Good to know. My regal tang baby came down with whitespot last week. I don’t have a QT. I’ve since purchased Selcon and garlic essential oil, I’ve used both to treat their food and upped the amount of feeding in a day. Within 5 days all spots have gone and the fish looks normal and healthy. So it is possible to suppress it even when the fish is quite far gone, but if this stuff actually manages to kill it then it would be a revelation in the hobby.
The fact that it isn’t already being shouted about from the rooftops though, makes me more than a wee bit dubious.