It's probably just me, but I never understood how pouring stuff in the coolant to plug small holes didn't negative affect the radiator which is...full of small holes.
I'd probably give the same explanation you've already heard so I'll forego it, but I can speak from my own experience it sealed up a leaky t-stat housing on my wife's car and its been holding for at least a year...the key is driving 25 miles or so after putting it in.
If you ask why I didn't just change the gasket, it's on a 4.6 and I didn't feel like pulling the intake.