My understanding is that coolant contains rust inhibitors and dissipates heat better (and the radiator may be sized to this assumption) as well as having a lower freezing point. I don't know enough about automotive fluids to know when to cut corners so I just use the right SAE shit. Besides, $50 once every 5 years is hard not to justify.
But for flushing I doubt you'd include coolant. It's madness, Johnny.
Far as I can tell I'm the only one in the thread a member of the faction who thinks that flushing a radiator means draining, filling with flushing product, draining, filling & draining to wash out, and then refilling with coolant. Others seem to think you're just draining and refilling, talking about what you should be running rather than using to flush. What are we talking about here? Actually flushing or just changing the coolant? Pls advise asap.