Perhaps you are aware of the info below, here is my review of thermocure, hope it is helpful.
You can use Thermocure instead, made by the same company, and is for cooling systems. Comes concentrated, put it in and add water. Since it is concentrated saves on shipping if you buy online. I've used it, left it in my A (radiator and block/head) for a couple of weeks and ran it as coolant. 1 bottle does about 2 treatments if just doing the radiator.
Since I had tons of rust, had to do multiple treatments. Once evaporust or thermocure is black like very used oil, it has lost its effectiveness. Leaving it in longer does not do more once it has turned black. Both are only active on rust, does not do anything to metal/hoses, rubber/etc.. I do not believe it will work on scale. It leaves a soft grey very thin coating, which eventually flushes away, but can turn your coolant with a slight grey tinge to it. With use the coating will flush off over time.
If you have a horrible radiator, there is the possibility that it will leak after use. But that would be due to that you have pinholes/bad-cracked solder joints that are blocked/sealed by rust scale, and have removed the rust/scale. This happened to me on 1 of the two radiators I've used this stuff on.
When I drained it out, drained it into a large tub, and then filtered it. Very little debris, no flakes, a teaspoon or less of grit. Bac flushed it and got a little more grit. So the majority of the rust "dissolved" into the liquid. The grit may not have been rust since it was not brown/black. Could have been casting sand, or scale that loosened up. I have seen one reviewer who indicate he got a few flakes. Best practice after draining is to backflush thoroughly before flushing. Reduce the chances of clogging the radiator.